trig
posted by Alex .
Okay, I've been getting some of these, but I can't seem to verify this identity... any help? Here's the problem
Sin(x+y) + Sin(xy) = 2sinxcosy
Okay, I've been working on the left side, and distribute, getting:
Sinx + Siny + Sinx  Siny
And, the sinx's add up to the 2sinx that I need for the right side, but the siny's cancel out if I don't change them around. So I changed one of them to 1/cscy... but I can't seem to work with that and the other siny to end up with cosy.
Where did I go wrong, or where do I go with it now?

Sin(x+y) = Sin(x)Cos(y) + Cos(x)Sin(y)
If you replace y by minus y and add you get twice the first term, because
cos(y) = cos(y) and sin(y) =  sin(y). 
oh, dang, forgot about that identity!
Okay, well, adding that up it ends up as 2sinx2cosy... but I need it to be 2sinx(1)cosy.
or am I really tired and I'm thinking too out of the box to realize the entire term of 2sinxcosy consists of 2sinx's and 2cosy's?
if not, what do I switch up to drop a cosy to satisfy the right side of the equation? oh man, am i sure forgetting everything about math, lol.
Respond to this Question
Similar Questions

Simplifying with Trigonometry Identities
Hi, I am a senior in High School having a really difficult time with two problems. I have to prove using the trigonometric identities that they equal each other but I am having a really hard time trying to get them to equal each other. … 
Trigonometry.
( tanx/1cotx )+ (cotx/1tanx)= (1+secxcscx) Good one! Generally these are done by changing everything to sines and cosines, unless you see some obvious identities. Also generally, it is best to start with the more complicated side … 
trig
it says to verify the following identity, working only on one side: cotx+tanx=cscx*secx Work the left side. cot x + tan x = cos x/sin x + sin x/cos x = (cos^2 x +sin^2x)/(sin x cos x) = 1/(sin x cos x) = 1/sin x * 1/cos x You're almost … 
Trig
Sin(Xy)sin(x+y)=sin^2 x  sin^2 y work on one side only...so i worked on the right =(sinxsiny)(sinx+siny) does that equal sin(xy)sin(x+y)? 
trig!!
Sin(Xy)sin(x+y)=sin^2 x  sin^2 y work on one side only...so i worked on the right =(sinxsiny)(sinx+siny) does that equal sin(xy)sin(x+y)? 
TRIG!
Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6 x=1  (3/4)sin^2 2x work on one side only! Responses Trig please help!  Reiny, Monday, February 23, 2009 at 4:27pm LS looks like the sum of cubes sin^6 x + cos^6 … 
Trig
Simplify sin x cos^2xsinx Here's my book's explanation which I don't totally follow sin x cos^2xsinx=sinx(cos^2x1) =sinx(1cos^2x) =sinx(sin^2x) (Where does sine come from and what happend to cosine? 
PreCalc : Verify the Identity
Verify the Identity: sin(x+π)/cos(x+3π/2) =tan^2xsec^2x I've done: sinxcosπ+cosxsinπ / cosxcos(3π/2)  sinxsin(3π/2) sinx(1) + cosx(0) / cosx(0) sinx(1) sinx/sinx What do I do from here? 
Precalculus/Trig
I can't seem to prove these trig identities and would really appreciate help: 1. cosx + 1/sin^3x = cscx/1  cosx I changed the 1: cosx/sin^3x + sin^3x/sin^3x = cscx/1cosx Simplified: cosx + sin^3x/sin^3x = cscx/1cosx I don't know … 
Trig Identities
Prove the following identities: 13. tan(x) + sec(x) = (cos(x)) / (1sin(x)) *Sorry for any confusing parenthesis.* My work: I simplified the left side to a. ((sinx) / (cosx)) + (1 / cosx) , then b. (sinx + 1) / cosx = (cos(x)) / (1sin(x)) …