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.
Graph of `y = 4x^4 + 15x^2 - 4`
The two intersections with the x-axis are at `x = -0.5` and `x=0.5`.
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