Question

求教一道数学题！附图！！！

希望解答者详细写下解题过程谢了！！！

Answer 1

由sin^2(A)+cos^2(A)=1,得(sin^2(A)+cos^2(A))^2=sin^4(A)+cos^4(A)+2sin^2(A)cos^2(A)=1 已知sin^4(A)+cos^4(A)=5/9,得2sin^2(A)cos^2(A)=1-5/9=4/9，sin^2(A)cos^2(A)=2/9，因A在三象限，则sin(A)cos(A)>0,sin(A)cos(A)=根号2/3