Solving Quadratic Equations

Solve by factoring, square root method, and quadratic formula

Solving Quadratic Equations

Standard Form

ax2+bx+c=0ax^2 + bx + c = 0

Method 1: Factoring

Example: x2+5x+6=0x^2 + 5x + 6 = 0

Factor: (x+2)(x+3)=0(x + 2)(x + 3) = 0

Solutions: x=2x = -2 or x=3x = -3

Method 2: Square Root Method

For x2=kx^2 = k: x=±kx = \pm\sqrt{k}

Method 3: Quadratic Formula

x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

The discriminant b24acb^2 - 4ac determines number of solutions:

  • Positive: 2 real solutions
  • Zero: 1 real solution
  • Negative: no real solutions

📚 Practice Problems

1Problem 1easy

Question:

Solve by factoring: x25x+6=0x^2 - 5x + 6 = 0

💡 Show Solution

Step 1: Factor the quadratic Find two numbers that multiply to 6 and add to -5: 2-2 and 3-3

x25x+6=(x2)(x3)=0x^2 - 5x + 6 = (x - 2)(x - 3) = 0

Step 2: Set each factor equal to zero x2=0orx3=0x - 2 = 0 \quad \text{or} \quad x - 3 = 0

Step 3: Solve each equation x=2orx=3x = 2 \quad \text{or} \quad x = 3

Answer: x=2x = 2 or x=3x = 3

2Problem 2medium

Question:

Solve using the quadratic formula: x2+6x+2=0x^2 + 6x + 2 = 0

💡 Show Solution

Identify: a=1a = 1, b=6b = 6, c=2c = 2

Use the quadratic formula: x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Step 1: Calculate the discriminant b24ac=(6)24(1)(2)=368=28b^2 - 4ac = (6)^2 - 4(1)(2) = 36 - 8 = 28

Step 2: Substitute into the formula x=6±282x = \frac{-6 \pm \sqrt{28}}{2}

Step 3: Simplify 28\sqrt{28} 28=47=27\sqrt{28} = \sqrt{4 \cdot 7} = 2\sqrt{7}

x=6±272=2(3±7)2=3±7x = \frac{-6 \pm 2\sqrt{7}}{2} = \frac{2(-3 \pm \sqrt{7})}{2} = -3 \pm \sqrt{7}

Answer: x=3+7x = -3 + \sqrt{7} or x=37x = -3 - \sqrt{7}

3Problem 3medium

Question:

How many real solutions does x2+4x+5=0x^2 + 4x + 5 = 0 have?

💡 Show Solution

Use the discriminant to determine the number of solutions: Discriminant=b24ac\text{Discriminant} = b^2 - 4ac

For x2+4x+5=0x^2 + 4x + 5 = 0: a=1a = 1, b=4b = 4, c=5c = 5

b24ac=(4)24(1)(5)=1620=4b^2 - 4ac = (4)^2 - 4(1)(5) = 16 - 20 = -4

Since the discriminant is negative, the equation has no real solutions (it has 2 complex solutions).

Answer: No real solutions