Question

a²+ab=4,-ab-b²=-5,则a²-b²=_,2a²+5ab+

Answer 1

a²+ab=4,

-ab-b²=-5,ab+b²=5

两式相加得

a²-b²=-1

两式相减得a²+2ab+b²=9

2a²+5ab+3b²

=2(a²+2ab+b²)+(ab+b²)

=2×9+5

=23