化简 cos(@-兀/2)/sin(5兀/2+@)*sin(@-2兀)*cos(2兀-@)

化简 cos(@-兀/2)/sin(5兀/2+@)*sin(@-2兀)*cos(2兀-@)
化简 cos(@-兀/2)/sin(5兀/2+@)*sin(@-2兀)*cos(2兀-@)

化简 cos(@-兀/2)/sin(5兀/2+@)*sin(@-2兀)*cos(2兀-@)
用sin(2π+a)=sina
cos(2π+a)=cosa
sin(π/2+a)=cosa
cos(a-π/2)/sin(5π/2+a)*sin(a-2π)*cos(2π-a)
=sina/sin(π/2+a)sinacosa
=sin²acosa/cosa
=sin²a

1/(cos@)^2

由诱导公式
cos(@-兀/2)/sin(5兀/2+@)*sin(@-2兀)*cos(2兀-@)
=sin@/cos@*sin@*cos@
=sin²@