identities Definition and 416 Threads

1. (A) sin(-x) = - sin x (C) cos(x+y) = cosxcosy - sinxsiny (B) cos(-x) = - cos x (D) sin(x+y) = sinxcosy + cosxsiny Use these equalities to derive the following trigonometric identities. a. absolute value of cos x/2 = \sqrt{}1 + cosx/2 b. absolute...

Hello. How can I prove something like \nabla\cdot(\mathbf fv)=(\nabla v)\cdot\mathbf f+v(\nabla\cdot \mathbf f) using only the definition of divergence \text{div}\mathbf V=\lim_{\Delta v\rightarrow0}\frac{\oint_S\mathbf V\cdot d\mathbf s}{\Delta v}, i.e. without referring to...

Trig substitition--lost in identities Homework Statement \int\frac{dx}{x^{2}\sqrt{x^{2}+1}} Homework Equations It's pretty obvious that this is a trig substitution problem requiring use of tangent. The Attempt at a Solution x=tan\theta dx=sec^{2}\theta x^{2}=tan^{2}\theta...

[tan(pi/4+x)-tan(pi/4-x)]/[tan(pi/4+x)+tan(pi/4-x)]=2sinxcosx I tried to prove this trig identity but I an really stuck. I think tan of pi/4 is '1', and if I do that then my numerator becomes zero, thus zero=2sinxcosx. But that can't be right, so I don't know what to do now. LS=...

I am learning how to prove conditional identities like (a^2-c^2+b^2+2ab)/(c^2-a^2+b^2+2bc) = (s-c)(s-a) if a+b+c = 2s - Derived from Herons formula I have understood the proof for the above , but i want more problems to work on. Can anyone suggest some link where i can find similar...

Homework Statement I'm not looking for anyone's pity, but I can't even begin to tell you how confused I am with this concept. My teacher spent all of five minutes teaching it to us and then leaves us to fend for ourselves with this ridiculously hard worksheet. Please help. 1. 2cscx =...

Homework Statement cosx - cosy=-2 sin(x + y/2) sin(x - y/2) Homework Equations dont know what identities to use The Attempt at a Solution ok so when i figure it out, the RHS always comes out to either... (cos x sin y - sin x cos y)/2 or just cos x sin y - sin x cos y...

Homework Statement Prove using index notation that, the x denoting a cross-product. (del x f del g)=del f x del g Homework Equations The Attempt at a Solution dif etc. denote partial derivatives. RHS=eijkdjfdkg LHS-I'm not even quite sure how to write it in index...

Homework Statement 1) sin(x+y)sin(x-y)=cos^2y-cos^2x 2) tan(∏⁄4+x)+tan(∏/4-x)=2sec2x 3) cosx-cosy=-2sin(x+y/2)sin(x+y/2) 4) 2cotx-2tanx=4-2sec^2x/tanxHomework Equations all trig identitiesThe Attempt at a Solution 1) i understand that i should show what i have attempted but there is way too...

Homework Statement How do I put the sign for pi and the sign for theta? I can not solve this problem. Please help because I am new and I am having difficulty in my precalculus homework. The problem says identify identities of: sin (pi/2 + theta) = cos theta...

hello, i am supposed to show that Sigma of k = 0 to m, (n, k) (n - k, m - k) = 2^m (n, m) So I have after expanding: (n, k) = n!/(n-k)!k! and (n-k, m-k) = (n-k)!/(m-k)!(n-m)! so together the (n-k)! cancels out and I have n!/k!(m-k)!(n-m)! and that is n!/m!(n-m)! which is (n, m)...

Vector Identities ?? Having heaps of trouble with v.identities any help possible would be greatly appreciated. Let F = (z,y,-x) and f = |F| <--- (magnitude F) Use vector identities to calculate; \nabla \cdot (f \nabla \times (f F))

Homework Statement Question One: Prove that |u x v|^2 = (u . u)(v . v)-(u . v)^2 where u and v are vectors. Question Two: Given that u = sv + tw, prove algebraically that u . v x w = 0 where u, v and w are vectors and s and t are integers. Homework Equations I don't know :( The...

How do i solve this trig question? identities etc? 4*[cos(B) + 3*sin(B)]=1+ 2*[3*sin(39) - cos(39)] i can get it to cosB + 3sinB=0.08054076 using basic algebra, but how do i find a value for B

Homework Statement The vectors F and G are arbitrary functions of position. Starting w/ the relations F x (∇ x G) and G x (∇ x F), obtain the identity ∇(F . G) = (F . ∇)G + (G . ∇)F + F x (∇ x G) + G x (∇ x F) Homework Equations The Attempt at a Solution I started off...

Homework Statement Use the definitions of Helmholtz free energy, F, and Gibbs free energy, H, together with the thermodynamic identity, to show that S = -(\frac{\partial F}{\partial T})_V and S = -(\frac{\partial F}{\partial T})_P Then use those definitions again, and the...

Homework Statement The problem is essentially (I've rephrased it, but this is what it is asking) show that [ (2n1cosa) / (n2cosa + n1cosb) ]2 is equal to (sin2a sin2b) / (sin2(a+b)cos2(a-b)) where these are for refraction through materials and satisfy n1sina=n2sinb 2. The...

Please help me in these identities! I tried to solve these identities, but I don't think that these are identities exept the first, 1.) sin2α/1+cos2α=tanα 2.) 1-cosα/sinα=tanα/2 3.) tanα+ctanα=csecα 4.) 3cosα+cos3α/3sinα-sin3α=3/2 5.) sin18°+sin30°=sin54 At first i did this...

I was wondering if anyone could help me out about trig identities. I'm a HS trig teacher and I'm going "by the books" and instructing them to manipulate the left and right sides of the identity independently of each other. They are not to treat it like an equation, e.g. no moving terms from...

Homework Statement Prove the following identities. a) cosx/1-sinx = secx + tanx b) cos^2x+ sinxcosx/tanx = 2cos^2x The Attempt at a Solution Well what I tried doing was substituting the appropriate compound angle formulas, double angle formulas, quotient identities, and...

Everyone knows the obvious trig identities like sin^2 + cos^2 =1, cosx=1+ sin^2, and tanx =sin/cos. I ran across an old identity the other day: 3cos^2(3x)+3sin^2(3x)=3. Can anyone here figure out why and how? I tried it and couldn't figure it out.

Hi Helpers:blushing:, the following is my problem: I have to rearrange Equation(1) to make Equation(2) using trigonometric identities (1): E(θ)=2Eo + (ΔR)^2 (c(x)cos^2(θ-θo) + c(y)sin^2(θ-θo)) (2): E(θ)=2Eo + ½(ΔR)^2 ((c(x)-c(y))cos(2(θ-θo)) + (c(x) + c(y)) I was able to get...

Is it always possible to prove combinatorial identities in a brute force way, as opposed to the preferred way of seeing that the RHS and LHS are two different ways of counting the same thing? For example, the identity \left (^{n-1}_{k-1}\right) + \left (^{n-1}_{k}\right) = \left...

Homework Statement Prove that sin (a+b) does not equal sin a + sin b. Let a = pi/3 and b = pi/6 Homework Equations The Attempt at a Solution Where I am lost is how to figure out what pi/3 or pi/6 is. Like for example, how can I know sin pi/3 is sqrt3 over 2? Is this a...

Hi, I'm confused about using trig identities. Homework Statement Match the trigonometric function with one of the following: (a) -1, (b) cos(x), (c) cotx (d) 1, (e) -tan(x), (f) sin(x) (1-cos^2x)(cscx) Homework Equations None that I know of. The Attempt at a Solution I multiply it...

Homework Statement Be x an element in the interval [Pi/4, 3Pi/4] express cos(2x), sin x, sin (x+pi) in terms of x. You must know that, for this question, cos x = z and z will always be < 0. Homework Equations cos(2x) = 2 (cos(x))^2 - 1 cos(2x) = cos^2 x - sin ^2 x sin^2 x + cos ^2 x = 1...

Homework Statement cos(\pi-x)= -cosX the formula is cos(A-b) = cosAcosB+sinAsinB so i sub in the given to get.. cos\picosx + sin\pisinX then where do i go from there? I am new to math like this, its a much higher level than what I am used to, any help would be very apprieciated...

Homework Statement Solve for x using half-angle identities cos (x/2) = -√2 / 2 Homework Equations cos(x/2) = ± √(1+cosx)/2 The Attempt at a Solution I am trying to figure out what to do with the identity, but I have no idea how to start. I know that x = 270 degrees or 3pi/2, but I do not...

Homework Statement I have this integral to solve: \int \frac{ab}{a^2 cos^2 t + b^2 sin^2 t} dt The limits are 0 to 2*pi. Homework Equations The Attempt at a Solution I've tried using trigonometric identities, trigonometric substitution... and many kinds of algebraic...

Homework Statement I have been given these two equations: x=2acos^2(x) , y = 2a(cos(x))(sin(x)) where a ranges from 0 to 5 and -2π < x < 2π I need to prove that these equations (when you plug in values for x) create points that when plotted, give you a circle with center (x-a) and radius a...

Homework Statement prove: cos^2(x)= (1+cos2x)/(2) Homework Equations i broke the cos^2(x) down to 1-sin^2(x)? The Attempt at a Solution

Homework Statement prove that cos ((pi/2)-x) = sinx Homework Equations The Attempt at a Solution i extended it to: (cos pi/2) (cos -x) + (sin pi/2) (sin -x) =1-sinx

exam coming up...need some help with these identities for practise. prove the following: A) \frac{tan^3x}{1+tan^2x}+\frac{cot^3x}{1+cot^2x}=\frac{1-2sin^2xcos^2x}{sinxcos} B) sec^6x-tan^6x=1+3tan^2xsec^x C) cos^4x=\frac{3}{8}+\frac{1}{2}cos2x+\frac{1}{8}cos4x D)...

Hi there, I am struggling to solve for x in the following problem:- Find all values of x in the interval 0<= x <= 360 for which: tan^2(x) = 5sec(x) - 2 I have used the identity tan^2(x) + 1 = sec^2(x) to get: sec^2(x) - 1 = 5sec(x) - 2 and rearranged to get sec^2(x) - 5sec(x) +...

Homework Statement a) If c is a number and \sum a_{n} from n=1 to infinity is convergent to L, show that \sum ca_{n} from n=1 to infinity is convergent to cL, using the precise definition of a sequence. b)If \sum a_{n} from n=1 to infinity and \sum b_{n} from n=1 to infinity are convergent...

[SOLVED] Convergent Series Identities Homework Statement a) If c is a number and \sum a_{n} from n=1 to infinity is convergent to L, show that \sum ca_{n} from n=1 to infinity is convergent to cL, using the precise definition of a sequence. b)If \sum a_{n} from n=1 to infinity and \sum...

Hi all Teacher gave me homework that i am having trouble doing it .. i need help in these two problems which i can't seem to solve. how can i prove the following : @= theta sec@ + tan@ = tan@sec@ cot@ + cos@ and sin^2@ - tan@= tan^2@ COS^2@ - cot@ my try is...

Theres a few... Write each expression as a single trigonometric ratio or as the number 1. 1) sint+(cott)(cost) 2) (sec x)(sin^2x)(csc x) For number one I went like this: sin t + ((1/cot)(cos/1)) sin t + (cos t/cot t) sin t + (cos t/1)( sin t/cos x) (sin t cos t)/1 + (sin t cot...

Prove the following identities: (cos A = cos B)^2 + (sin A + sin B)^2 = 2[1+cos(A-B)] I'm really a mess at this stuff. I missed a few important days and fell behind, so I don't reeeally know what to do when things start getting squared and whatnot., but I tried! :bugeye: Left Side...

Homework Statement Prove: \int\left(\nabla \times \vec{F}\right)\cdot d\vec{V} = \oint \left(\vec{\hat{n}} \times \vec{F} \right) dS Homework Equations In the previous part of the question, we proved that: \nabla \cdot \left( \vec{F} \times \vec{d} \right) = \vec{d} \cdot \nabla...

Homework Statement I'm on the last section of identities entitled half angle identities. This one seems to give me some trouble because I have never encountered one with a horizontal shift in it. Tips? tan 1/2( ß + π/2 ) = ( 1 + sin ß ) / cos ß

The question states, "Prove the identity." (1) cos(x + y) cos(x-y) = cos(^2)x – sin(^2)y. Should i start off using the addition and subtraction formulas for the LHS, and breaking down the perfect square for the RHS? If not or if so, how would I go about solving this problem? Step by step...

I just don't get this stuff. I've been trying on my own with the book. Also, is there a better way to post this? Homework Statement tanx 1 + secx _________ + _________ = 2csc x 1 + secx tanx I need to prove that this side equals the other. Homework...

I'm solving a pretty descent trig identity question, but I'm stuck. I'm not going to type out the original question, but here the section that I'm stuck on: sin^4x + cos^4x and here is what I have to prove: 1-2sin^2xcos^2x I know that I'm really close, I just can't get this section. Any help...

[SOLVED] Question involving trigonometric identities and inverse functions Homework Statement http://img141.imageshack.us/img141/2651/quiz1question5zi8.jpg Homework Equations I've tried to combine the following known equations to come up with a solution: \frac{d}{dx}(sin^{-1}x) =...

First I wanted to say hello, that I'm new to the forum, and very glad to have found you! I am having a terrific time with verifying my trig identities. I have done ALL odd probs in my text, and am repeating them. The problem that I am having is that I do not see a clear path from one side of...

Hello this one has stumped me for about a day and I have tried several different approaches. maybe someone could point me in the right direction. cot^2x-1/1+cot^2x=2Cos^2x-1 I startedon the Left side tring to prove the equation. cot^2x-1/csc^2x using Pyth. Theory...

Anyone know if the difference of cos^2 and sin^2 is some obscure identity that no one's heard of? Edit: nevermind. Shaum's tells me that cos^2 - sin^2 = cos(2a). GO SHAUMS!

Homework Statement 1. Calculate: \nabla \times (\frac{\vec{p} \times \vec{r}}{r^{3}}) in cartesian and spherical coordinates, where \vec{p} is a constant vector. 2. Calculate surface integrals: \int \vec{r} (\vec{a} \cdot \vec{n}) dS \int \vec{n} (\vec{a} \cdot \vec{r}) dS where...

http://oakroadsystems.com/twt/ I searched and it looked like no one had posted this before, so here it is. Trig without tears is an awesome site in which some guy explains trigonometry, from the basic functions of sine and cosine to the double and half angle identities. The interesting part...