π/6≤2x+π/6≤7π/6
问题描述：
π/6≤2x+π/6≤7π/6
怎么等于
-1/2≤sin(2x+π/6)≤1
答
设y＝2x+π/6,则π/6≤y≤7π/6,
根据正弦函数的图像可以看出,-1/2≤siny≤1