# b/((b+4)(b-4)) + 10/((b-9)(b+4)) its asking me to add these fractions by finding the LCD and I need help ?

## List item

Feb 21, 2017

See below.

#### Explanation:

$\frac{b}{\left(b + 4\right) \left(b - 4\right)} + \frac{10}{\left(b - 9\right) \left(b + 4\right)}$

Both denominator have the factors $\left(b + 4\right) \left(b - 4\right) \left(b - 9\right)$ so

multiplying and dividing both fractions for it we have

$\frac{1}{\left(b + 4\right) \left(b - 4\right) \left(b - 9\right)} \left(\frac{b \left(b + 4\right) \left(b - 4\right) \left(b - 9\right)}{\left(b + 4\right) \left(b - 4\right)} + \frac{10 \left(b + 4\right) \left(b - 4\right) \left(b - 9\right)}{\left(b - 9\right) \left(b + 4\right)}\right) = \frac{b \left(b - 9\right) + 10 \left(b + 4\right)}{\left(b + 4\right) \left(b - 4\right) \left(b - 9\right)}$

and finally

$\frac{b}{\left(b + 4\right) \left(b - 4\right)} + \frac{10}{\left(b - 9\right) \left(b + 4\right)} = \frac{{b}^{2} + b + 40}{\left(b + 4\right) \left(b - 4\right) \left(b - 9\right)}$