1、a²+b²
=a²+2ab+b²-2ab
=(a+b)²-2ab
=5²-2×4
=25-8
=17
2、这个题目有问题还有一道有时间求看一下——求方程x的平方-4乘y的平方-x+2y-4等于0的整数解(x+2y)(x-2y)-(x-2y)=4(x-2y)(x+2y-1)=4∴x-2y=-4 x-2y=-2 x-2y=-1x-2y=1 x-2y=2x-2y=4x+2y-1=-1 x+2y-1=-2x+2y-1=-4x+2y-1=4 x+2y-1=2x+2y-1=1∴x=-2 x=-3/2x=-2 x=2x=3/2x=2y=1y=1/4y=-1/2y=1/2 y=-1/4 y=-1∴有两对整数解x=-2，y=1和x=2，y=-1