已知sina*cosa=3/8，且pai/4
sina*cosa=3/8 => -2*sina*cosa=-3/4 Cos^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=1/4 Cosa-Sina=1/2 ..多动下脑子。。逻辑不难啊