What two fractions have unlike denominators but the lcd is not the product of the denominators?

If the denominators are (x + 4) and (x^2 - 16)
The LCD would be (x^2 - 16) which is NOT the product of the two denominators.

5/(x + 4)  + 6/ (x^2 - 16)

5(x - 4) /(x^2 - 16)  +    6/(x^2 - 16)
Does this make sense to you? If not ask more questions.