Question

已知a分之b=-3,求a的平方-3ab-4b的平方分之a的平方-2ab-3b的平方的值

Answer 1

(a^2-2ab-3b^2)/(a^2-3ab-4b^2)

=[(a-3b)(a+b)]/[(a-4b)(a+b)]

=(a-4b+b)/(a-4b)

=1+b/(a-4b)

=1+(b/a)/[1-4(b/a)]

=1+(-3)/[1-4(-3)]

=1+(-3)/13

=10/13