Cube both sides:

Equating coefficients, we find and . Looking quickly, I realize that if , the system of equations is solved. Hence,

For the next one, do the same thing:

Square both sides:

Equating coefficients, we have and

Let's solve for in the equation on the right: (we know because otherwise, ).

Plugging that into the first equation:

Hence, or . Since must be a rational number, it cannot be the first one, so . Then .

Before, we found . So, if , then . If , then .

So,

Checking on a calculator, you find it is .