已知:X+Y=8,XY=15,求下列各式的值(1)x^2+y^2, (2)(x-y)^2过程要详细,谢谢_数学解答

已知:X+Y=8,XY=15,求下列各式的值(1)x^2+y^2, (2)(x-y)^2
过程要详细,谢谢

人气：473 ℃　时间：2020-06-15 11:45:36

解答

(1)x^2+y^2
=x^2+y^2+2xy-2xy
=（x+y)^2-2xy
=8^2-2*15
=64-30
=34
(2)(x-y)^2
=x^2+y^2-2xy
=(x^2+y^2+2xy)-4xy
=(x+y)^2-4xy
=8^2-4*15
=64-60
=4