cos(π/4+x)=3/5化简得：√2/2(cosx-sinx)=3/5即：cosx-sinx=3√2/5同时平方：(cosx-sinx)²=1-sin2x=18/25所以sin2x=7/25因为sin2x=2sinxcosx=7/25,cosx-sinx=3√2/5解得sinx=√2/10或sinx=-7√2/10因为7π/12...