T=10π=2π/w∴ w=1/5∴ f(x)=2cos[(1/5)x+π/6]f﹙5α+5π/3﹚=2cos(α+π/3+π/6)=-6/5即 -2sinα=-6/5即 sinα=3/5,则 cosα=4/5f（5β-5π/6）=2cos(β-π/6+π/6)=16/17即 cosβ=8/17,则sinβ=15/17cos(α+β)=...