f(x)=2sin(x/3-30°)=2sin(x/3-π/6)(1)f(5π/4)=2sin(5π/12-π/6)=2sinπ/4=√2.(2)f(3α+π/2)=2sin(α+π/6-π/6)=2sinα=10/13、sinα=5/13、cosα=12/13、tanα=5/12.f(3β+π/2)=2sin(β+π/6-π/6)=2sinβ=6...f(3α+π/2)=2sin(α+π/6-π/6)这步是怎么得到的？f(3α+π/2)=2sin[(3α+π/2)/3-π/6]=2sin(α+π/6-π/6)