Question

若a减b等于5，a乘b等于4，则a的平方加b的平方等于多少，a加b等于多少

Answer 1

a-b=5
两边平方
a²-2ab+b²=25
所以a²+b²
=25+2ab
=25+2*4
=33

(a+b)²
=a²+b²+2ab
=33+2*4
=41

Answer 2

(a-b)*(a-b)=a*a+b*b-2*a*b=25
(a+b)*(a+b)=a*a+b*b+2*a*b
思路就是这样