Question

已知sina-cosa=-5/4,则sinacosa=

Answer 1

(sina-cosa)^2=25/16=sin^2 (a)+cos^2(a)-2sin(a)cos(a)

sin^2 (a)+cos^2(a)=1 所以2sin(a)cos(a)=-9/16

sin(a)cos(a)=-9/32