cos(π/2-α)-sin(π/2+α)=1/5
sina-cosa=1/5
平方得
(sina-cosa)^2=(1/5)^2
sin^2a+cos^2a-2sinacosa=1/25
1-2sinacosa=1/25
sinacosa=12/25
sin(π+α)cos(π+α)
=sinacosa
=12/25
cos(π/2-α)-sin(π/2+α)=1/5
sina-cosa=1/5
平方得
(sina-cosa)^2=(1/5)^2
sin^2a+cos^2a-2sinacosa=1/25
1-2sinacosa=1/25
sinacosa=12/25
sin(π+α)cos(π+α)
=sinacosa
=12/25