# What is Unknowns: Definition and 155 Discussions

The Tomb of the Unknown Soldier is a monument dedicated to deceased U.S. service members whose remains have not been identified. It is located in Arlington National Cemetery in Virginia, United States. The World War I "Unknown" is a recipient of the Medal of Honor, the Victoria Cross, and several other foreign nations' highest service awards. The U.S. Unknowns who were interred are also recipients of the Medal of Honor, presented by U.S. presidents who presided over their funerals. The monument has no officially designated name.

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1. ### Trying to impress my 8th grade students, made some unknown stuff

I had previously collected small amount of hydrogen to explode as an attention getting opener for my 8th grade science students when we started chemistry. My third period kids are inquisitive and hard working and also wanted a bigger explosion, so I thought I would try to reward their effort. I...
2. ### B What is the “Unknown physics” of the new Kilonovae explosion?

Scientists recently observed a kilonovae explosion. To their surprise, the explosion is completely spherical. They are saying that this is the cause of unknown physics but I don’t understand why they think unknown physics is causing this. What’s unknown about a perfect spherical explosion? My...
3. ### Misc. Finding "Stuff": Surfing for Unknowns with Element13

How do you search for something if you don't know what its called? Are there any websites that one can surf through and look for "stuff"? I don't know how else to phrase the question but, for example; if the website sold electronic stuff it would have an Electronics menu button under which it...
4. N

### Find Two Numbers -- Have Two Equations and Two Unknowns

Two numbers add up to 72. One number is twice the other. Find the numbers. Let x and y be our two numbers. Two numbers add to 72. x + y = 72 One number is twice the other. I can use x or y for this next set up. x = 2y Here is the system: x + y = 72 x = 2y You say?
5. ### How Do You Solve Equations with Variables V, U, and T?

Hi, I'm new to the forum so I'm not so sure if I've formatted this correctly :p I don't really know where to start with the question above as there are three unknowns (v, u, and t). Answer is 0.53s or 1.9s - I'm so grateful for any help. Many thanks.
6. ### MHB Direct solution for two unknowns in two equations

I am writing a computer program to solve a physical problem which at some part involves the following two equations and two unknowns; (1) $C_1(x^4-y^4) + C_2x = Q_1$ (2) $C_1(y^4-x^4) + C_3y = Q_2$ C1, C2 & C3 are coefficients which can readily be calculated and do not rely on knowing...
7. ### A Solving a differential equation with two unknowns

One thing that is given in paper (attached) is a operating set point for temperature which is given as 20 for day and 16 for night but I do not know whether its initial condition for temperature or not. Can anyone please guide me that what kind of equation is it and how can I solve it with these...
8. ### How can we solve for both T₂ and m in a system with multiple unknowns?

Here are two questions for my online homework. In part (a) we have to find T₁, T₂, and m. For part a, I drew a free body diagram and used that ΣFₓ = -30N +T₁cos(60) = 0 To find T₁ = 60N. The software accepted my answer. Now we have to find T₂ and m. We have ΣFᵧ = T₂ + T₁sin(60) + mg = 0. We do...
9. ### Solve for the total Kinetic Energy change with unknowns

Firstly I tried defining into an equation to make the whole thing more 'tangible'. ##m_1= Paula's~Weight⋅2 = m_p⋅2## ##m_2= \frac {Dave's~weight}{2} = \frac {m_d}{2}## Before impact ##E_k1= \frac 1 2 (m_p⋅2)(0^2)## ##E_k1= \frac 1 2 (2m_p)## ##E_k1= m_p ## After Impact ##E_k2= \frac 1 2...
10. ### A Diffusion equation and a system of equations with reciprocal unknowns?

So the normal diffusion equation looks like \frac{\partial c}{\partial t} = k\frac{\partial}{\partial x}\left(\frac{\partial c}{\partial x}\right) I know how to get explicit and implicit solutions to this equation using finite differences. However, I am trying to do the same for an equation of...
11. ### Linear Equations: Solving for 3 unknowns given 3 equations

a+b=0 so.. a= -b -2a-2c = -1 = -2(-b)-2c = -1 = 2b-2c=-1 -a-3b+c= 1 = -(-b)-3b+c= 1 = b-3b+c=1 = -2b+c=1 i think this is right but i don't know where to go from here
12. ### I Solving 2 equations and 2 unknowns with vectors

Hi, I have a work-related problem to solve and I'm not sure where to start and a pointer would be appreciated. I have the following two sets of polar equations V1 + V2 = Vx V1 + V2 + V3 = Vy, where Vx, V3, and Vy have been measured with reasonable accuracy, maybe +/-2% Any thoughts on how to...
13. ### Acceleration needed to keep an object from sliding down a windshield

I think I am on the right path but I'm having trouble cancelling out the mass of the wallet. I drew a free body diagram and know that there are three forces acting on the wallet: gravity, friction, and normal force (including the van's acceleration). The y-component of the friction and normal...
14. ### Equilibrium problem with 5 unknowns

Homework Statement This is an equilibrium problem with 3 unknown forces, and 2 unknown angles. I have resolved the horizontal and vertical forces. Homework Equations Horizontal components of forces: -W1cos Θ + W3cos ∅ = 0 Vertical components: W1sin Θ + W3sin ∅ - W2 = 0 Where W1, W2, W3...
15. ### Beam calculation with 3 unknowns

Homework Statement A 5m metal beam is supported on 2 supports. The beam is 30kg and the man is 65kg. The man stands at A, to prevent the beam tipping extra weights have been placed at B. Find reaction forces and the weights that have been placed at B. Take acceleration due to gravity to be...
16. ### I Can Complex Equations Break the Bounds of the Unit Circle?

Is doing the same thing repeatedly... Can I spin out of the unit circle with the solution to this equation: (a^2 + b^2) / (a * b - a / b) = (a / b + b / a) Extra Credit for a refutation. Hint: signal processing.
17. ### Principal stresses 3D, solving for direction cosines n1,m1,n1

Homework Statement -4.882L1+M1+2N1=0 L1-2.882M1=0 2L1-0.882N1=0 L1^2+M1^2+N1^2=1 How to solve for L1 ,M1 and N1 ? 0<L1,M1,N1<1Homework EquationsThe Attempt at a Solution
18. ### Plotting a graph to find unknowns

Homework Statement Plot a suitable graph, using your x and y data, to find the variables a and b. Homework Equations y = ax + bx^2 The Attempt at a Solution This is clearly a quadratic, the best I can do is to play about with lns and I came out with lny = lnax + lnbx^2 lny = ln(ab.x^3) lny =...
19. ### Solving trigonometric equation of a sum of unknowns

Homework Statement \sin (x) = \frac{2}{3} and \sec (y) = \frac{5}{4}, where x and y lie between 0 and \frac{\pi}{2} evaluate \sin (x + y) Homework Equations Looked over some trig laws, don't think I saw anything that's too relevant. There \sec (x) = \frac{1}{\sin (x)} The Attempt at a...
20. ### I The concept of 'unknowns' in equations

You can solve an equation with one unknown. You need two different equations for two unknowns, and so on. This implies a binary distinction between 'known' and 'unknown'. But are there grades or shades of unknown? For instance, if you know that a variable is negative but not its magnitude, can...
21. ### Regular heptagon, finding value of unknowns

Homework Statement Homework Equations (n-2)*180[/B]The Attempt at a Solution 11.a: 7-2=5, 5*180= 900. 900/7= 128.57 degrees b. How do you find the unknowns?[/B]
22. ### MHB Find unknowns in equation going from perfect square? to quadratic format?

Hi all I'm trying to work out how to answer this type of problem. (6x+2z)^2-64=(ax+2z+8)(-8+bx+cz) where a, b and c > 0 I have attempted the problem by expanding the brackets: =36x^2+24xz+4z^2-64 This is the same as (6x+2z)^2-(8)^2 Then subtracting from either 'side' of the quadratic and...
23. ### Postulations and unknown unknowns in physics

My understanding is that scientific proof, if we mean physics not pure mathematics, is all about "postulations" to explain experiment, observation, and data. But these set of consistent postulations that give us elegant charming equations have their limits of applications and run into anomalies...
24. ### Is it possible to calculate the unknowns in these equations?

Well folks, I am a bit confused with this apparently "simple" system of equations. pa=Probability player A wins a point when he is on serve qa=1-pa=Probability player A loses a point when he is on serve pb, and qb are the same for player B when he is on his own serve I have calculated the...
25. ### Definable relationships between 4 variables with 2 equations

Hi, I saw a derivation in a book and I don't see the logical connection. Suppose 1.\ \ a=b \text{ and } 2.\ \ x=y Then 3.\ \ a-b= \lambda (x-y) makes sense to me since 0=\text{Anything}⋅0 However they said "similarly" 4.\ \ a+b= \mu (x+y) , and this I don't understand. To me a+b= 2a...
26. ### MHB Kirchoff's Law equation 3 unknowns Help

Please could somebody help me with this Kirchoff's law question with explanations/working out? I've been on it for hours and cannot see where I'm going wrong! Q. An electrical circuit comprises three closed loops giving the following equations for the currents i1, i2 and i3. i1 + 8i2 + 3i3 =...
27. ### What is the Missing Piece in Solving for ρ in this Simple Problem?

Homework Statement The total energy for a Van der Waals bonded solid is: E=-\frac{A}{r^6}+B*e^{-\frac{r}{\rho}} where the 1st and 2nd terms are for attraction and repulsion respectively, A and B are constants, r is the inter-atomic distance, and \rho is the range of interaction (i.e...
28. ### Load on a beam: More unknowns than equations?

Homework Statement Homework Equations FBD and all forces and moments = 0 The Attempt at a Solution Sketched in the image. So, I don't know how to go on with my analysis of the load, since I can't determine the reaction forces. Can someone please help me? Thanks in advance!
29. ### MHB Diophantine Equations With Three Unknowns Online

Hi! ?? ? ? ? ?? True method?
30. ### 2D conservation of Energy and Momentum with *Three* unknowns

Homework Statement A 2.0 kg ball moving with a speed of 3.0 m/s hits, elastically, an identical stationary ball as shown. If the first ball moves away with angle 30 ° to the original path, determine a. the speed of the first ball after the collision. b. the speed and direction of the second...
31. ### Solution for two unknowns with two equations

lb*cos(qb) - lc*cos(qc) = ld*cos(qd) - la*cos(qa) lb*sin(qb) - lc*sin(qc) = ld*sin(qd) - la*sin(qa) Those are the equations I have. I know all the parameters but qb and qc. How can I solve for qb and qc ?
32. ### MHB How to calculate with two unknowns

How to calculate with two unknowns. Solve.. 4x-5y=7 3y-2x=1
33. ### Solving a system in five unknowns for lagrange multiplier

Homework Statement I have to find the extrema of a given function with two constraints f(x,y,z) = x+y+z;x^2-y^2=1;2x+z=1 The Attempt at a Solution If I create a new function F then I have F(x,y,z,\lambda,\mu)=x+y+z-(x^2\lambda - y^2\lambda -\lambda) -(2x\mu + z\mu -...
34. ### Pressure Drop Testing - Too Many Unknowns?

Hello there, I am having a discussion with a co-worker about a pressure drop test. I have two different 'boxes' for which I don't know the pressure drop. What I want to know is the difference in pressure drop between the two 'boxes'. Knowns 1) PA1 = PA2 = PA = Inlet Pressure for...
35. ### Partial Fractions - 3 Unknowns

Hello, i've come across a partial fractions problem that I don't know how to solve - Usually, the denominator of the fraction I need to split up into two separate fractions is a quadratic, but in this instance it's a cubic. Specifically, the problem I'm having is that two of the factors to...
36. ### How to solve a system with more unknowns than equations?

Because if you reduce to Row-Echelon form you don't end up with a triangulated form. Here is what I ended up with (How do I use Latex Reference to construct a Matrix? Can someone help me with that by the way please?) 1 -1 3 2 | 1 0 1 1 3 | -1 0 0 1 1 | -1
37. ### Row Reduction to solve for 6 Unknowns

Homework Statement I am in a calculus class where we are learning the introduction to row reduction. I have done this before in other courses, so I am familiar with the process, but I am not sure about this one. We were given: x4 + 2x5- x6 = 2 x1 + 2x2 + x5 -x6 = 0 x1 + 2x2 + 2x3 - x5 +...
38. ### Help solving for 3 equations and 3 unknowns

Homework Statement Solve the following equation for P_{1} and P_{2} Homework Equations 7.0+0.004P_{1}-\lambda(1-0.0004P_{1})=0 7.0+0.004P_{2}-\lambda=0 P_{1}+P_{2}-500-0.0002P_{1}^{2}=0The Attempt at a Solution I am having some issues on ways to solve this problem. I guess the main point I am...
39. ### Help with solving three equations with 3 unknowns

I have the three following equations in the file attached: 1. 70000000=(((R1^3)*4/3)-((R2^3)*4/3 "))(100*cosα))/(2(R1 -R2)(pi/2)(R1^4-R2^4) + 100sinα/ ((pi/4)(R1^4-R2^4)) 2. 120000000=((100*sinα))/(R1^2-R2^2)+ (100*cosα*R1 )/((pi/4)(R1^4-R2^4)) 3. m=100(pi)(R1^2-R2^2 )(cosα)* R1...
40. ### MHB Determine the degree of each equation in each of the indicated unknowns.

$xy+yz+xz+z^2x=y^4$ x;y;z; x and z; y and z; x, y, and z I know x is 2nd degree, y is 4th degree, z is 2nd degree. but I don't know how to determine the degree of the combinations of the unknowns. please help. thanks!
41. ### System of Equations with Two Unknowns, Algebra Help

Homework Statement I have two equations with two unknowns. I know m, F, R, r and I. I need to find a and f. m = 2 F = 28 R = 0.25 I = 0.0625 r = 0.1875 I know the ultimate answers are a = 16\frac{1}{3} and f = 4\frac{2}{3} Homework Equations (1) Fr-fR=I\frac{a}{R} (2)...
42. ### Solving for Unknowns in Conservation of Energy and Momentum Equations

Homework Statement Could someone help me get from these two equations to E'/E=[(A-1)/(A+1)]2 http://postimg.org/image/m5zi9ha19/ Homework Equations E = v^2=E' = v'2 + AV^2 p=v=p' = v' + AV = v from conservation of energy, momentum E'/E= (v'2 + AV^2)/(v^2) The Attempt at...
43. ### A system of 2 non-linear equations with 2 unknowns

Homework Statement i'm trying to find a solution for these two equations, p & q are variables and c is known constant (it's given randomly) :  \begin{align}...
44. ### Equation with two unknowns in complex exponential

hello friends, when i build the mathmatical model of robot,i face a new question that i ever seen before. i have a reverse kinematic lever as the leg and i want to use the tip position to get the relationship of fold angle and rotate angle reversely here is my equation: x*e^iθ - y*e^iθ *...
45. ### MHB Inequality proof w/ induction, 2 unknowns

I am given a statement to prove: Show (without using the Binomial Theorem) that $$(1+x)^n\geq{1+nx}$$ for every real number $$x>-1$$ and natural numbers $$n\geq{2}$$. I am given a hint to fix $$x$$ and apply induction on $$n$$. I started by supposing $$x$$ is a fixed, real number larger than -1...
46. ### No problem, glad I could help! :smile:

Homework Statement In the following problem, find conditions on a and b such that the system has no solution, one solution, and infinitely many solutions. x + by = -1 ax + 2y = 5 Homework Equations None that I know of. The Attempt at a Solution Basically, first I put the entire...
47. ### Three equations and three unknowns: fitting a function.

Hi! I'm doing a project with sound, and exploring modulation. I got stuck on an intermediate step ... and can't solve a simple algebra problem. I have a wave, which I know the envelope is a perfect sine wave, and fits the following three equations: A * cos( ph1 ) = knownSlope1 A *...
48. ### How Can You Solve Systems of Four Equations with Four Unknowns?

Homework Statement Hello, Although this could be labeled as an EE problem, this is more of an Algebra problem. Anyways, I am having a very hard time solving for the following 4 equations with 4 unknonws. 269.0 = R1*(R2+R3+R4)/(R1+R2+R3+R4) 267.8 = R2*(R1+R3+R4)/(R1+R2+R3+R4)...
49. ### Nodal Analysis Help, 1 equation 2 unknowns

1. 2. V=IR, Nodal analysis 3. Based on where I have drawn my ground, V2=-10V, V1=3I. From this I should just have 1 equation with 1 unknown (if I have done this correct). My KCL equation for node V1 is (V3+10)/8 + (V3-3I)/2 + V3/12. I am stuck, I need to find an equation for I in...
50. ### MHB Solving Linear Systems with "m Equations & n Unknowns

My book describes a linear system with "m equations in n unknowns." Maybe this is a subtle detail but this confuses me. Shouldn't it be the other way around, "n unknowns in m equations?"