# Math Help - Find cos(a-b)

1. ## Find cos(a-b)

Given that

sin(a)+cos(b)= (3^(1/2))/2 and

sin(a)+sin(b)=3/2

Find cos(a-b).

Can anyone help me?

2. ## Re: Find cos(a-b)

You should know that $\displaystyle \cos{(\alpha \pm \beta)} \equiv \cos{(\alpha)}\cos{(\beta)} \mp \sin{(\alpha)}\sin{(\beta)}$.

What can you do with this?

3. ## Re: Find cos(a-b)

It may also be good to remember that $\cos^{2}(x) + \sin^{2}(x) = 1$

4. ## Re: Find cos(a-b)

The answer i get is 0.786... but the answer given is 0.5. What answer do you guys get?

5. ## Re: Find cos(a-b)

How did you arrive at that? Please describe your process and let's check it out.