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 .
Checking on a calculator, you find it is .