a²+ab=4,-ab-b²=-5,则a²-b²=_,2a²+5ab+3b²=_.请给讲解,尽快,

a²+ab=4,-ab-b²=-5,则a²-b²=_,2a²+5ab+3b²=_.请给讲解,尽快,
a²+ab=4,-ab-b²=-5,则a²-b²=_,2a²+5ab+3b²=_.请给讲解,尽快,

a²+ab=4,-ab-b²=-5,则a²-b²=_,2a²+5ab+3b²=_.请给讲解,尽快,
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

a²+ab=4→a×(a+b)=4
-ab-b²=-5→b×(a+b)=5
a²-b²=(a+b)×(a-b)=4-5=-1
a/b=4/5→(4b/5+b)×(4b/5-b)=-1→b²=25/9
2a²+5ab+3b²=2×(4b/5)²+5×(4b/5)×b+3b²=207/25b²=23