Question

正余弦和差化积公式

Answer 1

sinα+sinβ = 2sin[(α+β)/2] cos[(α-β)/2]

sinα-sinβ = 2cos[(α+β)/2] sin[(α-β)/2]

cosα+cosβ = 2cos[(α+β)/2] cos[(α-β)/2]

cosα-cosβ = -2sin[(α+β)/2] sin[(α-β)/2]