`4x^4+15x^2=4`, so


Let `u=x^2` to make things easier. Then we have:





So `u=1/4` or `u=-4`.

But `u=x^2`, so

`x^2=1/4` or `x^2=-4`

`x=+-1/2` are the only real solutions.

Once again, let's have a look at the graph of the function, to better understand the situation. This time it's `y = 4x^4 + 15x^2 - 4`.

The intersection with the x-axis will tell us the solution for the original equation.

0.51-0.5-151015-5xyOpen image in a new page

Graph of `y = 4x^4 + 15x^2 - 4`

The two intersections with the x-axis are at `x = -0.5` and `x=0.5`.

Easy to understand math videos: