It might looks simple, but it's a real challenge. In fact, if

, then f has 2 zeros. It means that the solution is not singular. But to prove it... not easy.

. We want to study its sign. So we want to find when it is equal to

.

.

Now if

. It means that

is decreasing from negative infinite to

. As when

,

,

is increasing from

to positive infinite.

f(0)=-4. As it will increase (strictly), it must cross the x axis on a single point when

. You can find a similar conclusion calculating for example

. It means that the roots of f are respectively between

and

. (5 because

). Now to find the roots, you can say that there is an easy one to see, when

. To calculate the other root, I suggest you the bisection method which will work.