Quadratic Formula

intermediatealgebraquadratic equations

Solves any quadratic equation of the form ax² + bx + c = 0

The Formula

x = (-b ± √(b² - 4ac)) / (2a)

Variables & Symbols

a

Coefficient of x²

b

Coefficient of x

c

Constant term

x

Unknown variable (solution)

When to Use This Formula

  • When solving quadratic equations
  • When factoring is difficult or impossible
  • To find roots of parabolic functions
  • In physics problems involving projectile motion

Worked Examples

Example 1

Problem:

Solve x² + 5x + 6 = 0

Solution: x = -2 or x = -3

Step-by-Step:

1

Identify: a=1, b=5, c=6

2

Calculate discriminant: b² - 4ac = 25 - 24 = 1

3

Apply formula: x = (-5 ± √1) / 2

4

x = (-5 + 1)/2 = -2 or x = (-5 - 1)/2 = -3

Example 2

Problem:

Solve 2x² - 7x + 3 = 0

Solution: x = 3 or x = 0.5

Step-by-Step:

1

Identify: a=2, b=-7, c=3

2

Calculate discriminant: 49 - 24 = 25

3

Apply formula: x = (7 ± 5) / 4

4

x = 12/4 = 3 or x = 2/4 = 0.5

Common Mistakes to Avoid

  • Forgetting the ± symbol (missing one solution)
  • Miscalculating the discriminant
  • Dividing by a instead of 2a
  • Sign errors when b is negative

Historical Context

The quadratic formula was known to ancient Babylonians around 2000 BC. The modern algebraic form was developed by Arab mathematicians in the 9th century.

Real-World Applications

1

Calculating projectile trajectory in physics

2

Optimizing profit and cost functions in economics

3

Determining antenna parabola dimensions in engineering

4

Calculating maximum height of thrown objects

Practice Problems

Problem 1: Solve x² + 3x - 10 = 0

Show Answer

Answer: x = 2 or x = -5

Problem 2: Solve 3x² + 8x - 3 = 0

Show Answer

Answer: x = 1/3 or x = -3

Problem 3: Solve x² - 6x + 9 = 0

Show Answer

Answer: x = 3 (double root)

Tags:

algebraequationsquadraticrootspolynomial

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