The general form of a quadratic equation is a*x^2 + b*x + c = 0.

Define a function that when passed the coefficients a, b and c and a fourth boolean attribute flag, returns,

1. null, if no solution exists (that's why the return type is Double, not double)

2. the higher of the two roots of the equation, if flag is true and solution exists.

3. the smaller of the two roots of the equation, if flag is false and solution exists. You can use the built-in Math.max, Math.min and Math.sqrt functions. NOTE: The challenge of this question is in the research and not the implementation.