Solving a Cubic Equation

Write a program that finds every real root of the cubic equation $Ax^3 + Bx^2 + Cx + D = 0$.

Every equation in the input has at least one integer root.

$A$, $B$, $C$, and $D$ are integers between -2,000,000 and 2,000,000, and $A$ is not 0. Every root is between -1,000,000 and 1,000,000. Two different roots of the same equation differ by more than $10^{-4}$.

The first line contains the number of test cases $N$ ($0 < N < 100$). Each of the next $N$ lines contains the coefficients $A$, $B$, $C$, and $D$ of one equation, separated by spaces.

For each test case, print every real root of the equation in ascending order on one line. Round each root to four decimal places and put a single space between consecutive roots. Print a repeated root only once. A root that rounds to zero is written 0.0000, with no sign.

No root falls exactly on a rounding boundary at the fifth decimal place, so the rounding direction is never ambiguous.