trig exercise of sums and differences identities

Question

If cosα=0.173 and cosβ= 0.432 with both angles’ terminal rays in Quadrant-I, find the values of cos(α+β)=?

cos(α-β)=?

Your answers should be accurate to 4 decimal places.

please help! thanks !

Answer 1

Use formula

cos(α-β)=cos(α)cos(β)+sin(α) sin(β).

if sin(α)=√(1-cos²(α))