Question

Sendo x e y arcos do primeiro quadrante, senx = 1/3 e cosy = 1/5, calcule o valor de cos (x - y).

Answer 1

senx = 1/3 => cosx = √(1 - cosx²)
=> cosx = √8/3

cosy = 1/5 => seny = √(1- cosy²)
=> seny = √24/5

cos(x-y) = cosx . cosy + senx . seny

= √8/3 . 1/5 + 1/3 . √24/5
= √8/5 + √24/5


=> (√8 + √24) / 15 <=