Question

已知a+b=-7 ab=12 ,求a^2+b^2-ab和(a-b)^2的值

Answer 1

a^2+b^2-ab
=a^2+b^2+2ab-3ab
=(a+b)^2-3ab
=(-7)^2-3*12
=49-36
=13

(a-b)^2
=(a+b)^2-4ab
=(-7)^2-4*12
=49-48
=1