simplify the experession

**cm3pyro** · Apr 16th 2008, 06:51 PM

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

**Mathstud28** · Apr 16th 2008, 07:04 PM

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

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

**cm3pyro** · Apr 16th 2008, 07:36 PM

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

**Mathstud28** · Apr 16th 2008, 07:41 PM

Originally Posted by cm3pyro

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

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

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