Mathematics
Grade 12
15 min
Solve a quadratic equation using the quadratic formula
Solve a quadratic equation using the quadratic formula
Tutorial Preview
1
Introduction & Learning Objectives
Learning Objectives
Identify the coefficients a, b, and c from a quadratic equation in standard form.
State and correctly apply the quadratic formula to find the roots of any quadratic equation.
Calculate the discriminant and use it to determine the nature and number of roots (real, complex, or repeated).
Solve quadratic equations that yield rational, irrational, and complex roots.
Simplify radical and complex-number solutions into their standard forms.
Rearrange a given quadratic equation into the standard form ax^2 + bx + c = 0 before applying the formula.
Recognize when the quadratic formula is the most efficient method for solving a quadratic equation compared to factoring or completing the square.
How can you find the exact time an object thrown in the air will hit th...
2
Key Concepts & Vocabulary
TermDefinitionExample
Quadratic Equation in Standard FormAn equation of the second degree, meaning it contains a term with a variable raised to the power of 2. The standard form is ax^2 + bx + c = 0, where a, b, and c are constants and a ≠ 0.The equation 3x^2 - 7x + 2 = 0 is in standard form.
CoefficientsThe numerical constants that multiply the variables in a polynomial. In ax^2 + bx + c = 0, 'a' is the leading coefficient, 'b' is the linear coefficient, and 'c' is the constant term.In 5x^2 + 0x - 9 = 0, a = 5, b = 0, and c = -9.
Roots (or Zeros)The solutions to a quadratic equation. These are the values of x for which the equation equals zero, and they represent the x-intercepts of the corresponding parabola on a graph.For x^2 - 4 = 0, the roots are x = 2 a...
3
Core Formulas
The Quadratic Formula
x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
This formula provides the solution(s) for x in any quadratic equation written in the standard form ax^2 + bx + c = 0. It is a universal method that works for all quadratic equations, regardless of whether they are factorable.
The Discriminant and Nature of Roots
\Delta = b^2 - 4ac
The value of the discriminant (Δ) tells you the number and type of roots without fully solving the equation:
1. If Δ > 0, there are two distinct real roots.
2. If Δ = 0, there is exactly one repeated real root.
3. If Δ < 0, there are two complex conjugate roots.
5 more steps in this tutorial
Sign up free to access the complete tutorial with worked examples and practice.
Sign Up Free to ContinueSample Practice Questions
Challenging
For what range of values of k does the equation 2x² - 3x + k = 0 have two distinct real roots?
A.k < 9/8
B.k > 9/8
C.k < 8/9
D.k > 8/9
Challenging
If r and s are the roots of the quadratic equation 2x² - 8x + 3 = 0, what is the value of r² + s²?
A.16
B.10
C.13
D.4
Challenging
The height h (in meters) of a projectile is given by h(t) = -4.9t² + 50t + 1.5, where t is time in seconds. At what time t > 0 does the projectile reach a height of 100 meters? Solve using the quadratic formula.
A.t ≈ 2.58 s
B.t ≈ 7.62 s
C.t ≈ 2.58 s and t ≈ 7.62 s
D.The projectile never reaches 100 meters.
Want to practice and check your answers?
Sign up to access all questions with instant feedback, explanations, and progress tracking.
Start Practicing Free