sinx+cosx=2/3m 1式
sin^2x+cos^2x=1 2式
1式^2-2式
=>2sinxcosx=4m^2/9-1=>sinxcosx=2m^2/9-1/2
sin^4x+cos^4x=(sin^2x+cos^2x)^2-2sin^2x*cos^2x=1-2[2m^2/9-1/2]^2