cos(π/4+x)=4/5 x∈(-π/2,-π/4),sin(π/4+x)=-3/5 x∈(-π/2,-π/4),sinx=sin(π/4+x) cosπ/4- sin(π/4) cos(π/4+x)= (-7√2 )/10;cosx=√2 /10;（sin2x-2sin方x）/（1+tanx）=(2sinxcosx-2sinxsinx)/((cosx+s...