Question

已知abc为三角形的三边,sin(90°-α)*sinα+cos(90°-α)*cosα=1/3,求sin2α

Answer 1

sin(90°-α)*sinα+cos(90°-α)*cosα=1/3

cosαsinα+sinαcosα=1/3

所以sin2α=2sinαcosα=1/3