Originally Posted by
tami-chan87 Hi, I'm taking the a Math placement test this Saturday so I've been practicing for that, but here's a problem I just can't figure out:
If sin(x+y) = sinx cosx + cosx siny
find sin((pi/2)+αlpha).
The answer to this is supposed to be cos aplha, but I'm not sure how you get there.
I found a similar problem in one of my Math books so I substituted
((pi/2)+alpha) for x and y in the equation above. I got
sin((pi/2)+alpha) = sin(pi/2) cos alpha + cos (pi/2) sin alpha
then I went on to divide by sin(pi/2) and sin alpha
(sin(pi/2) + sin alpha)/(sin alpha + sin(pi/2)) = cos alpha + cos(pi/2)
the left side will cancel, right? So we have
1 = cos alpha + cos (pi/2)
pi/2 = 90degrees and cos 90degrees = 0, right?
so then
1 = cos alpha
Is that correct? what about the 1 on the left side? Can I just leave it there?