(sin10+sin50)/(sin35×sin55)的值详细过程详细

问题描述:

(sin10+sin50)/(sin35×sin55)的值详细过程详细
为什么sin10+sin50等于cos20?

sin10 + sin50
= sin(30-20) + sin(30+20)
= 2 * sin30 * cos20
= cos20
sin35 * sin55
= sin35 * cos35
= 1/2 * sin70
= 1/2 * cos20
∴ (sin10 + sin50) / (sin35 * sin55)
= cos20 / (1/2 * cos20)
= 2