Question

Find the least common denominator for these two rational expressions.

y/y^2 -1                 y/y^2 -8y+7

Answer 1

$\frac{y}{y^{2}-1},\ \frac{y}{y^{2}-8y+7}$
$=\frac{y}{(y-1)(y+1)},\ \frac{y}{(y-1)(y-7)}$
$=\frac{y(y-7)}{(y-1)(y+1)(y-7)},\ \frac{y(y+1)}{(y-1)(y+1)(y-7)}$

So the common denominator is $(y-1)(y+1)(y-7)$