y=sinx的减区间应该是[π/2 +2kπ,3π/2+2kπ](/是分数线的意思)
所以y=2sin(2x+π/6）的减区间是 2x+π/6∈[π/2 +2kπ,3π/2+2kπ]即
π/2 +2kπ=