Question

sin40。+sin80。=2sin60。cos20。计算过程

Answer 1

直接记公式，和差化积公式
sinθ+sinφ=2sin[(θ+φ)/2]cos[(θ-φ)/2]

sinθ-sinφ=2cos[(θ+φ)/2]sin[(θ-φ)/2]

cosθ+cosφ=2cos[(θ+φ)/2]cos[(θ-φ)/2]

cosθ-cosφ=-2sin[(θ+φ)/2]sin[(θ-φ)/2]

Answer 2

sin40+sin80
=sin(60-20)+sin(60+20)
=sin60cos20-sin20cos60+sin60cos20+sin20cos60
=2sin60cos20

Answer 3

这个就是和差化积公式
sina+sinb=2sin[(a+b)/2]cos[(a-b)/2]

Answer 4

sin40+sin80
=sin(60-20)+sin(60+20)
=sin60cos20-cos60sin20+sin60cos20+cos60sin20
=2sin60cos20