The discriminant b² − 4ac decides the type of answer: positive gives two real roots, zero gives one repeated root, negative gives a pair of complex roots.
The vertex — the parabola's highest or lowest point — is at x = −b ÷ 2a.
Common questions
How do I solve x² − 5x + 6 = 0?
Here a = 1, b = −5 and c = 6. The discriminant is 25 − 24 = 1, so x = (5 ± 1) ÷ 2, giving 3 and 2.
Can I enter decimals and negative numbers?
Yes. Use a minus sign for negative coefficients and either a decimal point or comma.