cos(x/2)+sin(x/2)=-√5/2[cos(x/2)+sin(x/2)]^2=(-√5/2)^2[cos(x/2)]^2+[sin(x/2)]^2+2cos(x/2)sin(x/2)=5/42cos(x/2)sin(x/2)=1/4sinx=1/4因为x在第二象限,所以cosx=-√15/4sin(2x)=2sinxcosx=-√15/8cos(2x)=(co...