Question

若a的2次方+ab=20,ab-b的2次方=-13.(1)求a的2次方+2AB-B的2次方的值（2）求a的2次方+3ab

Answer 1

解析

a²+ab=20

ab-b²=-13

(1)a²+2ab-b²=(a²+ab)+(ab-b²)

=20-13

=7

(2—）a²+3ab-2b²

=(a²+ab)+2ab-2b²

=(a²+ab)+2(ab-b²)

=20+2*-13

=20-26

=-6