Christopher G. answered 08/19/13
Math Tutor - Algebra, Trig, Calculus, SAT/ACT Math
The discriminant is the expression under the radical in the quadratic formula: b2 - 4ac, where the quadratic is of the form ax2 + bx + c. In this case, a = 2, b = 9, and c = 7.
b2 - 4ac = (9)2 - 4(2)(7) = 81 - 56 = 25
These are the rules for determining the nature of the roots of a quadratic based on the discriminant:
(1) If the discriminant = 0, then there is one real solution
(2) If the discriminant > 0, then there are two real solutions
(3) If the discriminant < 0, then there are two imaginary solutions
In this example, the discriminant = 25, which is greater than 0. Therefore, there are two real solutions to this quadratic equation.