# How do you add or subtract #(y^2-5)/(y^4-81) + 4/(81-y^4)#?

##### 1 Answer

We can rewrite this sum as

We can find the lowest common denominator, which, then, is

Using the l.c.d.:

That can be your final answer, but let's draw attention to the fact we have factorable functions there.

Let's find the roots of

Now, as for the denominator:

Let's just go slowly here and take the square root of both sides.

So, here, as we are dealing with a polinomial of 4

Therefore, your "final" answer can be rewritten as

Finalfinal answer, then: