(1)1.2345^2+0.7655^2+2.469*0.7655

问题描述:

(1)1.2345^2+0.7655^2+2.469*0.7655
(2)已知X+ 1/X=3,则X^+ 1/X^2 的值为?
(3)已知X-Y=4.X^2+Y^2=12 则XY的值为?
请写出具体的过程.

(1)1.2345^2+0.7655^2+2.469*0.7655 =1.2345^2+0.7655^2+2*1.2345*0.7655 =(1.2345+0.7655)^2=2^2=4(2)X+ 1/X=3(X+ 1/X)^2=X^2+ 1/X^2+2=9因此X^2+ 1/X^2=7(3)X-Y=4(X-Y)^2=X^2+Y^2-2XY=16以为X^2+Y^2=12 所以XY=-2...