Thread: simplify the experession

use the addition and subtraction formulas to simplify the experession

sin(x+y)sin(x-y)
write the answer in terms of sin x and cos y only

Originally Posted by cm3pyro

use the addition and subtraction formulas to simplify the experession

sin(x+y)sin(x-y)
write the answer in terms of sin x and cos y only

$\displaystyle sin(a+b)=sin(a)cos(b)+sin(b)cos(a)$ and $\displaystyle sin(a-b)=sin(a)cos(b)-sin(b)cos(a)$...now apply that

i did ..but i am coming up with the worng answer.

Originally Posted by cm3pyro

i did ..but i am coming up with the worng answer.

well since I am sure you know that $\displaystyle a^2-b^2=(a+b)(a-b)$ we have that case here...except in reverse...so it should be $\displaystyle sin(a)^2cos(b)^2-sin(b)^2cos(a)^2$