sin(π/2 +2a)/cos(π/4 +a)是否=2sin(π/4 +a)
问题描述:
sin(π/2 +2a)/cos(π/4 +a)是否=2sin(π/4 +a)
答
sin(π/2 +2a)/cos(π/4 +a)
=2sin(π/4 +a) cos(π/4+a)/cos(π/4 +a)
= 2sin(π/4 +a)
答
∵sin[π/2 +2a)]=sin[2(π/4 +a)]=2sin(π/4 +a)cos(π/4 +a)
两边同除cos(π/4 +a)得:
sin(π/2 +2a)/cos(π/4 +a)=2sin(π/4 +a)