已知0
sin(π/4+x)=cos[π/2-(π/4+x)]=cos(π/4-x)=12/13,cos(π/4-x)=cosπ/4cosx+sinπ/4sinx=(√2/2)cosx+(√2/2)sinx(√2/2)(sinx+cosx)=12/13,(1)对(1)式两边平方,(1+sin2x)=288/169,sin2x=119/169,0