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