-π/2sina+cosa=-1/5(sina+cosa)^2=(-1/5)^2sina^2+cosa^2+2sinacosa=1/251+2sinacosa=1/252sinacosa=-24/25(sina-cosa)^2=sina^2+cosa^2-2sinacosa=1+24/25=49/25丨sina-cosa丨=7/5∵ -π/2
sina+cosa=-1/5(sina+cosa)^2=(-1/5)^2sina^2+cosa^2+2sinacosa=1/251+2sinacosa=1/252sinacosa=-24/25(sina-cosa)^2=sina^2+cosa^2-2sinacosa=1+24/25=49/25丨sina-cosa丨=7/5∵ -π/2