1、y=3sin(2x-π/3）最大值为3,此时2x-π/3=2kπ+π/2 即x=kπ+5π/12 (k∈R)
2、cos(π+α）=-cosα=-3/5 cosα=3/5
cos(5π/2-α）=cos(π/2-α）=sinα=±4／5
tan(π+α）=tanα=±4／3
3、sinθ+cosθ=2sinα ∴1+2sinθcosθ=4sin²α
∴2sinθcosθ=4sin²α-1=2（2sin²α-1）+1=1-2cos2α
∵sinθcosθ=sin^2β ∴2sinθcosθ=2sin^2β=1-（1-2sin^2β）=1-cos2β
∴1-2cos2α =1-cos2β ∴2cos2α =cos2β ∴4cos²2α =cos²2β