x∈（兀/4,3兀/4）即sinx >cosxsinx+cosx=5/13√2那么平方得到(sinx)^2+2sinxcosx+(cosx)^2=50/169而(sinx-cosx)^2=(sinx)^2+(cosx)^2-2sinxcosx=2- 50/169=288/169所以sinx -cosx=12/13√2与sinx+cosx=5/13√2连立...