# Thread: Simplifying trigonometric expressions part 3

1. ## Simplifying trigonometric expressions part 3

I need help with these problems....

7. cos(x-y) if cosx=5/12 and cosy=11/12

8.tan(x=y)

2. Originally Posted by angelica2619
I need help with these problems....

7. cos(x-y) if cosx=5/12 and cosy=11/12

8.tan(x=y)
8. makes no sense. It is incomplete and contains a typo.

7. Compound angle formula: cos(x - y) = cos x cos y + sin x sin y.

Calculate sin x from cos x = 5/12. Calculate sin y from cos y = 11/12. Substitute everything into the above and simplify.