Yes. You can calculate the two roots of a quadratic equation by using the quadratic formula, and because there are square roots on the quadratic formula, and if the radicand is not a perfect square, so the answer to that equation has decimal.
That depends on the equation.
Because it's part of the quadratic equation formula in finding the roots of a quadratic equation.
By using the quadratic equation formula
To find the roots (solutions) of a quadratic equation.
If the quadratic is ax2 + bx + c = 0 then the product of the roots is c/a.
Using the quadratic equation formula or completing the square
If the discriminant of b2-4ac in the quadratic equation formula is less than zero then the equation will have no real roots.
If the discriminant of the quadratic equation is zero then it will have 2 equal roots. If the discriminant of the quadratic equation is greater than zero then it will have 2 different roots. If the discriminant of the quadratic equation is less than zero then it will have no roots.
When you need to find the roots of a quadratic equation and factorisation does not work (or you cannot find the factors). The quadratic equation ALWAYS works. And when appropriate, it will give the imaginary roots which, judging by this question, you may not yet be ready for.
The roots of the quadratic equation are the x-intercepts of the curve.