How do we rewrite 7/a - 9/b so that both terms have the denominator ab?

Answer 1

7 / a Multiply Numerator and Denominator by b

7 / a = 7 b / a b

9 / b Multiply Numerator and Denominator by a

9 / b = 9 a / a b

7 / a - 9 / b = 7 b / a b - 9 a / a b =

( 7 b - 9 a ) / a b