Question

If sin 42° =2/3, then cos 48°=

Answer 1

Sinα=cos(90-α)  is a basic identity.

if sin42=2/3 then cos(90-42)=2/3 as well  (90-42=48)

Answer 2

We know that:  sin Ф = cos(π/2 - Ф) ↔ sin Ф = cos(90° - Ф)
Then:

sin 42° = cos(90° - 42°) = cos 48°

IF sin 42° = 2/3, the cos 48° = 2/3