Question

Find the exact value of:

Cos(inverse tan 4/3 + inverse cos 5/13)

Answer 1

If the two angles are x and y,

cos(x+y) = cosx*cosy - sinx*siny

if tanx = 4/3,
cosx = 3/5
sinx = 4/5

if cosy = 5/13,
siny = 12/13

Now just plug and chug