
Tamara J. answered 05/20/13
Math Tutoring - Algebra and Calculus (all levels)
It's not clear whether the denominator is 1/(xy) + 1 or 1/(xy + 1).
In the case of the former, since we are essentially adding fractions we need to find a common denominator among them. Here, the common denominator is 'xy' so we need to multiply 1 by xy/xy then add the fractions in the denominator:
y/(1/(xy) + 1) = y/(1/(xy) + 1(xy/xy))
= y/(1/(xy) + (xy)/(xy))
= y/((1 + xy)/(xy))
When dividing by a fraction, multiply the numerator by the reciprocal of the denominator:
y/((1 + xy)/(xy)) = y((xy)/(1 + xy)
= (y·xy)/(1 + xy)
= xy2/(1 + xy)
In the second case, since we don't need to add any fractions we simply multiply the numerator by the reciprocal of the denominator:
y/(1/(xy + 1)) = y((xy + 1)/1)
= y(xy + 1)
= y·xy + y·1
= xy2 + y