a²+ab=4,-ab-b²=-5,则a²-b²=______,2a²+5ab+3b²=________.急,给讲解

a²+ab=4,-ab-b²=-5,则a²-b²=______,2a²+5ab+3b²=________.急,给讲解
a²+ab=4,-ab-b²=-5,则a²-b²=______,2a²+5ab+3b²=________.急,给讲解

a²+ab=4,-ab-b²=-5,则a²-b²=______,2a²+5ab+3b²=________.急,给讲解
a²+ab=4,-ab-b²=-5,则a²-b²=___-1___,2a²+5ab+3b²=___23_____.
a²-b²=a²+ab+(-ab-b²)=4+(-5)=-1
2a²+5ab+3b²=2(a²+ab)-3(-ab-b²)=2X4-3X(-5)=8+15=23

a²+ab=4，
-ab-b²=-5,
两式相加得a²-b²=-1
两式相减得a²+2ab+b²=9,
又ab+b²=5,
2a²+5ab+3b²
=2(a²+2ab+b²)+(ab+b²)
=2×9+5
=23