sin2α+根号3倍cos2α= 2sin(2α+π/3) = 1sin(2α+π/3) = 1/22α+π/3 = 5π/6α = π/4f(x)=2xcos(α-π/4)+sin(α+π/4) = 2x + 1a1 = 1a2 = 2+1a3 = 7an = 2^n - 1Sn = sum(2^n - 1)最后内个sum什么意思？