已知sin(a+π/4)=4/5,π/4

已知sin(a+π/4)=4/5,π/4
已知sin(a+π/4)=4/5,π/4

已知sin(a+π/4)=4/5,π/4
sin(a+π/4)=sinacos(π/4)+cosasin(π/4)=1/√2(sina+cosa)=4/5
sina+cosa=4√2/5 1+2sinacosa=32/25 sinacosa=7/50
sin^2a(1-sin^2a)=49/2500 sin^2a=0.02或0.98
由于π/4