What is Geometric: Definition and 808 Discussions

Geometry (from the Ancient Greek: γεωμετρία; geo- "earth", -metron "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space that are related with distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is called a geometer.
Until the 19th century, geometry was almost exclusively devoted to Euclidean geometry, which includes the notions of point, line, plane, distance, angle, surface, and curve, as fundamental concepts.During the 19th century several discoveries enlarged dramatically the scope of geometry. One of the oldest such discoveries is Gauss' Theorema Egregium ("remarkable theorem") that asserts roughly that the Gaussian curvature of a surface is independent from any specific embedding in an Euclidean space. This implies that surfaces can be studied intrinsically, that is as stand alone spaces, and has been expanded into the theory of manifolds and Riemannian geometry.
Later in the 19th century, it appeared that geometries without the parallel postulate (non-Euclidean geometries) can be developed without introducing any contradiction. The geometry that underlies general relativity is a famous application of non-Euclidean geometry.
Since then, the scope of geometry has been greatly expanded, and the field has been split in many subfields that depend on the underlying methods—differential geometry, algebraic geometry, computational geometry, algebraic topology, discrete geometry (also known as combinatorial geometry), etc.—or on the properties of Euclidean spaces that are disregarded—projective geometry that consider only alignment of points but not distance and parallelism, affine geometry that omits the concept of angle and distance, finite geometry that omits continuity, etc.
Originally developed to model the physical world, geometry has applications in almost all sciences, and also in art, architecture, and other activities that are related to graphics. Geometry also has applications in areas of mathematics that are apparently unrelated. For example, methods of algebraic geometry are fundamental in Wiles's proof of Fermat's Last Theorem, a problem that was stated in terms of elementary arithmetic, and remained unsolved for several centuries.

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  1. C

    MHB Understanding Geometric Sequences: Results & Formula

    Just a little help understanding results obtained. I have found the closed form of a sequence, but am a little unsure if there is a right way or can select either way of using the terms to create the explicit formula. I have found the common difference from the terms, which is 1.2, in my...
  2. S

    Probability Generating Function / Geometric

    Homework Statement a) P(X=x)=pq^x,\,x\geq 0 Find the PGF. b) P(X=x)=pq^{|x|},\,x\,\epsilon\,\text{Z} Find the PGF. 2. The attempt at a solution a) G_X(s)=E(s^X)=\displaystyle\sum_{x\geq 0}pq^x s^x=p\displaystyle\sum_{x\geq 0}(qs)^x=\frac{p}{1-qs} b) Not sure about this one... Is it: as...
  3. A

    Geometric Interpretation of √(x^2+y^2+z^2) and its Derivative

    Let r = √(x^2+y^2+z^2) One can easily show that \nablar= \vec{r}/r. But I'm having a hard time understanding what this means geometrically - who can help? :)
  4. S

    A geometric property of a map from points to sets?

    I'm interested in the proper way to give a mathematical definition of a certain geometric property exhibited by certain maps from points to sets. Consider mappings from a n-dimensional space of real numbers P into subsets of an m-dimensional space S of real numbers. For a practical...
  5. T

    Confused about the True Geometric Meaning of a Dot Product Answer.

    I have performed numerous calculations of dot products throughout my math courses, but I think I lack a fundamental understanding of what it actually means, beyond the abstract way I have been taught to deal with them. I know the definitions (it's the inner product, or the projection of A on to...
  6. D

    Geometric Understanding of Tensors.

    I am a beginner in theory of GR and am trying to understand it better. I have a problem with understanding tensors. I got the algebriac idea, incliding covariance, contravariance and transformations etc of tensors. But not the geometric. Tensors are abstract but can I not have geometric...
  7. L

    H/W help on Geometric vs Component Vector Addition

    Homework Statement Find y component of vector C from its length and the angle it makes with the x axis, that is, from geometry. Express the y component of vector C in terms of C and \phi. Homework Equations Vector addition using geometry: 1) C = \sqrt{A^{2}+B^{2}-2ABcos(c)}...
  8. L

    Geometric Meaning of a Vector Integral

    Hello everyone on these forums. :) If you would, please consider the 3-vector function r(t) = <f(t),g(t),h(t)>. What sort of geometric meaning can be assigned to the following integral? \int_a^b \vec{r}(t) dt = \left\langle \int_a^b f(t) dt, \int_a^b g(t) dt, \int_a^b h(t) dt\right\rangle...
  9. P

    Sign convention in geometric optics.

    Until today I learned in geometric optics that Object distance +ve for real object else -ve Image distance +ve for real image else -ve Radius of curvature +ve for if light comes to the surcace from the side lying center of curvature else -ve On the basis of this the lens formula...
  10. T

    What is the explanation for 2(xo)(yo) = 2?

    Homework Statement we had a a function on a graph of f(x)=1/x and then we are suposed to find the area of a triangle where the tangent line is the hypontenuse, and the x and y-axis are the base and hight...i found f'(x)= -1/x^2 from here i used the formula y-yo=x0(x-x0) and got that the x...
  11. M

    What is the Sum of a Geometric Series with a Given Initial Value and Ratio?

    Homework Statement I already counted V_{0}=-1 and q=\frac{1}{3} given: V_{n}=1-\frac{2}{U_{n}} Homework Equations count: \sum_{k=0}^{n}V_{k} The Attempt at a Solution i counted the sum and i got : ((\frac{1}{3})^{n+1}-1)(\frac{2}{3}) is that correct?
  12. C

    Limits, geometric series, cauchy, proof HELP

    i guys, I'm stuck on wording of a homework assignment and thought you might be able to help me. There are several questions... Consider the geometric series: (Sum from k=0 to infinity) of ar^k and consider the repeating decimal .717171717171 for these problems: Question 1: Find a formula...
  13. Z

    Geometric Series Question

    1. Homework Statement you are geometrically diluting/mixing 0.1 g of powder A with 100g of powder B, how many times do you have to mix the 2 together to finish the process? *each time you can only mix an equal portion of powder B to what you currently have mixed. Eg. 1:1 2:2 4:4 3...
  14. Z

    Geometric Dilution/Series

    Homework Statement you are geometrically diluting/mixing 0.1 g of powder A with 100g of powder B, how many times do you have to mix the 2 together to finish the process? *each time you can only mix an equal portion of powder B to what you currently have mixed. Eg. 1:1 2:2 4:4 The...
  15. W

    Zero-modified geometric dice problem

    Hi, I'm trying to come up with a probability for a game I play with a friend of mine. In the game, units "attack" by rolling six-sided dice; either 2 or 4 sides of the die count as a "hit" when rolled, depending on certain circumstances. The specific situation I am trying to figure out the...
  16. X

    Simplifying to a Geometric Series

    Homework Statement I have a question with asks to solve a differential equation via power series and I've done everything up to finding the recurrence relation which is a_{n+2} = -\frac{a_{n}}{n+2} Given the initial conditions a_{o} = 1 and a_{1} = 0 I'm trying to simplify the series into a...
  17. T

    Geometric sequences; solving algebraically for exponents

    Hello everyone! My question is twofold. Firstly, how do I solve for term numbers in a geometric sequence and secondly, how do I algebraically solve for variables that are exponents? Homework Statement Given the following geometric sequences, determine the number of terms, n. t1=5 r...
  18. V

    Geometric interpretation of an equation

    Homework Statement x,y, z are vectors in R^n. We have the equation: ax +by +cz, where a,b,c are constants such that a+b+c=1, and a,b,c>=0 What is the geometric interpretation of the equation? Homework Equations sv + tu, where u,v are vectors in R^n and s,t are constants such that...
  19. M

    Convergence Proof (As Part of Geometric Series Sum)

    Homework Statement I am trying to prove the sum of a geometric series, but one of the steps involves deriving this result: \lim_{n\to\infty}r^{n}=0 so that you can simplify the sum of a geometric series, where I have got to this stage: S_{\infty} = \frac{a(1-r^{\infty})}{1-r}...
  20. T

    First term of an infinite geometric sequence

    Homework Statement The sum of an infinite geometric sequence is 131/2, and the sum of the first three terms is 13. Find the first term. Homework Equations S∞ = a/(1-r) Sn = a-arn/(1-r) The Attempt at a Solution a/(1-r) = 131/2 a-ar3/(1-r) = 13 2a = 27-27r ...... 1 a-ar3 =...
  21. R

    Geometric Algebra: Is It Worth Studying for Physics?

    I've seen a number of books and articles touting Geometric Algebra as an important new area of math that will have large application to physics. Is there anything to these claims? Is it worth studying for a physics student?
  22. Rapier

    Sum of Geometric Series: Ʃ(3→∞) 3(.4)^(n+2)

    Homework Statement Find the sum of Ʃ(3→∞) 3(.4)^(n+2) Homework Equations Sum of Geometric Series = ao/(1 - r), ao=3, r = .4 = 2/5 The Attempt at a Solution I thought that I could use the definition of the sum of a geometric series (above) to determine the sum of this equation...
  23. T

    Geometric multiplicity of an eigenvalue

    Say we have an eigenvalue \lambda and corresponding eigenvectors of the form (x,x,2x)^T. What is the geometric multiplicity?
  24. F

    Dot product geometric proof question?

    Dot product proof question? Hi, I'm having trouble understanding the proof of the dot product in three dimensions (not using the cosine rule approach). Here's what I have for the 2D proof: u = u1 i + u2 j v = v1 i + v2 j u.v = u1v1 + u2v2 u.v = |u| |v| cos(θ) => u1v1 + u2v2 = |u| |v|...
  25. S

    Jordan Forms, Algebraic and Geometric Multiplicity

    Homework Statement A 20 × 20 matrix C has characteristic polynomial (λ^2 − 4)^10. It is given that ker(C−2I), ker (C − 2I)^2, ker (C −2I)^3 and ker (C −2I)^4 have dimensions 3,6,8,10 respectively. It is given that ker (C + 2I), ker (C +2I)^2, ker (C +2I)^3 and ker (C +2I)^4 have di- mensions...
  26. A

    Geometric representation of two-forms.

    I've been browsing through MTW recently and I found something that puzzles me: They claim that if you have two form, call it \mathbf{T}, it's value, say \mathbf{T}(\mathbf{u} , \mathbf{v} ) can be represented geometrically as follows: take two vectors \mathbf{u} and \mathbf{v}; the surface...
  27. marcus

    Loop bounce and geometric entropy (re: Bill A's question)

    Bill Alsept started a thread raising the general question---do cosmic models with regularly repeating big bangs conflict with thermodynamics' 2nd Law? (The law to the effect that, where it can be defined, entropy does not decrease, or does so only by rare accident, at irregular intervals if at...
  28. B

    Infinite Sum of a Geometric Series

    Homework Statement I feel bad asking another question after I just asked one yesterday, but I'm really close this time, I think! I have: \sum_{n=2}^{\infty}\frac{n^2-n}{2^n} And need to find the sum. Homework Equations \sum_{n=1}^{\infty}nx^{n-1}=\frac{1}{(1-x)^2} The Attempt at a...
  29. D

    Geometric Distribution Coin Flip

    Consider the following experiment: a coin that lands heads with probability p is flipped once; if on this first flip it came up H, it is then repeatedly flipped until a T occurs; else, if on the first...
  30. M

    Algebraic intuition vs geometric intuition

    This has been a curiosity of mine lately. I am wondering about what makes an algebra person an algebra person. I know geometers(at least it seems like it) seem to have a keen ability of spatial visualization. What characterizes the abilities of an algebra person? To clarify, I'm not just talking...
  31. S

    Exponential function and Geometric progression

    Can anyone help me answer this question? " Every exponential function is a geometric progression but not every geometric progression is an exponential function. Explain."
  32. J

    Convergence and Sum of the Geometric Series: A Quick Guide

    Geometric series problem urgent Homework Statement Calculate the geometric series of Ʃfrom n=1 to infinity of 1/n Homework Equations The Attempt at a Solution I don't know how to start solving, how can I solve this? I have test about this tomorrow I really need some help please.
  33. T

    Statistics: geometric distribution proof problem

    Statistics: geometric distribution "proof" problem Homework Statement If Y has a geometric distribution with success probability p, show that: P(Y = an odd integer) = \frac{p}{1-q^{2}} Homework Equations p(y)=p(q)^{2} The Attempt at a Solution p(1)=pq^0 p(3)=pq^2 p(5)=pq^4...
  34. B

    Geometric Interpretation of (lower) Cohomology?

    Hi, All: Just curious to know if there is an interpretation for lower cohomology that is as "nice", as that of the lower fundamental groups, i.e., Pi_0(X) =0 if X is path-connected (continuous maps from S^0:={-1,1} into a space X are constant), and Pi_1(X)=0 if X is...
  35. mnb96

    How to satisfy this identity (conformal model in geometric algebra)

    Hello, I have the following equation in x and y: xy - \sqrt{(x^2+a^2)(y^2+c^2)} = -\frac{1}{a^2}-\frac{1}{c^2} where the quantities a2 and c2 are given real constants, and I have to find real values for x, and y such that the equation above is always satisfied. Actually, I know that the...
  36. L

    Linear Algebra Geometric Planes

    For a homogeneous system of 3 equations in 3 unknowns (geometrically this is 3 planes in space all containing the origin) describe the relationship between the (three) geometric possibilities for the solution set and the number of free variables (non pivots) in RREF(A) where A is the...
  37. M

    Geometric Proof: Triangle Inequality Theorem for Point O | Homework Help"

    Homework Statement If O is any point inside a triangle ABC, prove that BA + AC > BO + OC. Homework Equations The Attempt at a Solution Any hints? Thanks...
  38. A

    Exploring Geometric Series Expansion with Higher Powers

    I need to find the solution to the geometric series expansion of the form... \sumn^2*x^n , for n=0,1,2,... most resources I've found only have answers for n*x^n or n*x^(n-1). I have no idea how to calculate this, so I was wondering if there's a book out there that has massive lists of...
  39. P

    Software for Calculating Geometric Transformations

    I am currently doing a course on Computer Graphics Algorithms. This involves lot of matrix transformations i.e. for eg - rotating co-ordinates, translating, reflecting etc. I am solving the problems on paper using a calculator, but I need some software which will help me verify the solution...
  40. Shackleford

    The three famous geometric construction problems

    We're covering this in my History of Mathematics class. I'm not entirely sure what they're asking.
  41. O

    Geometric Sequences and Series

    Homework Statement Q.: Show that if log a, log b and log c are three consecutive terms of an arithmetic sequence, then a, b and c are in geomtric sequence. Homework Equations Un = a + (n - 1)d and Sn = \frac{a(r^n - 1)}{r - 1} The Attempt at a Solution Attempt: Consider...
  42. O

    Geometric Sequences and Series

    Homework Statement Q.: The sum of the first five terms of a geometric series is 5 and the sum of the next five terms is 1215. Find the common ratio of this series. Homework Equations Sn = \frac{a(r^n - 1)}{r - 1} The Attempt at a Solution a + ar + ar^2 + ar^3 + ar^4 = 5 ar^5 +...
  43. O

    Sum to Infinity of a Geometric Series

    Homework Statement Q.: The numbers \frac{1}{t}, \frac{1}{t - 1}, \frac{1}{t + 2} are the first, second and third terms of a geometric sequence. Find (i) the value of t, (ii) the sum to infinity of the series. Homework Equations S\infty = \frac{a}{1 - r} The Attempt at a...
  44. O

    Sum to Infinity of a Geometric Series

    Homework Statement Q.: A geometric series has first term 1 and common ratio \frac{1}{2}sin2\theta. Find the sum of the first 10 terms when \theta = \frac{\pi}{4}, giving your answer in the form h - \frac{1}{2^k}, where h, k \in N. Homework Equations Sn = \frac{a(1 - r^n)}{1 - r}, when...
  45. M

    Find the sum of a geometric progression

    Homework Statement (1) \frac{1}{(1+x^{2})}+\frac{1}{(1+x^{2})^{2}}+...+\frac{1}{(1+x^{2})^{n}} The Attempt at a Solution (2)...
  46. G

    Calculus II - Infinite Series - Geometric Series

    Homework Statement Hi, I'm trying to solve the problem in the attachment. I was asked to evaluate the left hand side equation of the equal sign. I was unsure how to go about evaluating it so I consulted my solutions manual to look up the first step. The right hand side equation of the...
  47. O

    Sum to Infinity of a Geometric Series

    Homework Statement Q. Find the range of values of x for which the sum to infinity exists for each of these series: (i) 1 + \frac{1}{x} + \frac{1}{x^2} + \frac{1}{x^3} + ... (ii) \frac{1}{3} + \frac{2x}{9} + \frac{4x^2}{27} + \frac{8x^3}{81} + ... Homework Equations S\infty =...
  48. O

    Sum to Infinity of a Geometric Series

    Homework Statement Q. Find, in terms of x, the sum to infinity of the series... 1 + (\frac{2x}{x + 1}) + (\frac{2x}{x + 1})^2 + ... Homework Equations S\infty = \frac{a}{1 - r} The Attempt at a Solution S\infty = \frac{a}{1 - r} a = 1 r = U2/ U1 = (\frac{2x}{x + 1})/ 1...
  49. O

    Sum to Infinity of a Geometric Series problem

    Homework Statement Q.: A geometric series has first term a and common ratio r. Its sum to infinity is 12. The sum to infinity of the squares of the terms of this geometric series is 48. Find the values of a and r. Ans.: From textbook: a = 6, r = 1/ 2 Homework Equations...
  50. Telemachus

    Finding the Curve that Satisfies a Geometric ODE

    Hi there. I have this exercise in my practice for differential equations, and it asks me to find the curve that satisfice for every point (on the xy plane) the distance from (x,y) to the points of intersection for the tangent line and the x axis, and the normal with the x-axis remains constant...
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