Question

已知1/a+1/b=4,求（4a+3ab+4b)/(-3a+2ab-3b)的值

Answer 1

1/a+1/b=4

(a+b)/ab=4

a+b=4ab

（4a+3ab+4b)/(-3a+2ab-3b)

=[4(a+b)+3ab]/[-3(a+b)+2ab]

=(16ab+3ab)/(-12ab+2ab)

=19ab/(-10ab)

=-19/10