# Math Help - Prove that 2

1. ## Prove that 2

if coty = [sin (z + x)]/[cos(z-x) - cos (z+x)]
then prove that cotx, coty, cotz, are AP.

my incomplete of soln-
just converted cot y = cosy/siny

2. Try using $\displaystyle \sin{(\alpha \pm \beta)} \equiv \sin{(\alpha)}\cos{(\beta)} \pm \cos{(\alpha)}\sin{(\beta)}$

and $\displaystyle \cos{(\alpha \pm \beta)} \equiv \cos{(\alpha)}\cos{(\beta)} \mp \sin{(\alpha)}\sin{(\beta)}$

and see if you can simplify.

3. Originally Posted by Prove It
Try using $\displaystyle \sin{(\alpha \pm \beta)} \equiv \sin{(\alpha)}\cos{(\beta)} \pm \cos{(\alpha)}\sin{(\beta)}$

and $\displaystyle \cos{(\alpha \pm \beta)} \equiv \cos{(\alpha)}\cos{(\beta)} \mp \sin{(\alpha)}\sin{(\beta)}$

and see if you can simplify.
yeah done that but bcoming out of my control to solve it