trigonometric equation

Feb 2016
35
0
Mexico
If: sin(x+y)=k
Find sin(2x)=?

I did this:

I)sen2x=2senx.cosx

II)sen²x+cos²x=1
(senx+cosx)²-2senxcox=1
(senx+cosx)²-sen2x=1
(senx+cosx)² -1=sen2x


Considering cosx=y


(senx+y)² -1=sen2x
sen²x+2senx.y+y²-1=sen2x



Help?
 

chiro

MHF Helper
Sep 2012
6,608
1,263
Australia
Hey Isa16.

You should probably expand sin(x+y) first and isolate the x's from the y's.

Also - you won't have enough information since you have you two functions in two variables and only one piece of information (you need minimum two to get a solution).

Have you got any other information?