Question

已知sin a+cos a=m求cos a-sin a(45

Answer 1

sin a+cos a=m

(sin a+cos a)^2=m^2

(sin a)^2+(cos a)^2+2sinacosa=m^2

1+2sinacosa=m^2

2sinacosa=m^2-1

(cosa-sina)^2

=(sin a)^2+(cos a)^2-2sinacosa

=1-(m^2-1)

=2-m^2

45