已知sina*cosa=3/8，且pai/4<a

热心网友

sina*cosa=3/8 = -2*sina*cosa=-3/4Cos^2(a)+Sin^2(a)=1 :学数学都知道Cos^2(a)-2*sina*cosa+Sin^2(a)=1-(3/4)(Cosa-Sina)^2=1/4Cosa-Sina=1/2..多动下脑子。。逻辑不难啊