Find the roots of x^2 - 6x + 8.

• A. x = -2 or x = -4
• B. x = 3 or x = 5
• C. x = 2 or x = 4
• D. x = 0 or x = 6

Answer: (C)

Factoring a quadratic to find its roots. For x^2 - 6x + 8, look for two numbers whose product is 8 and whose sum is -6. Those numbers are -2 and -4, since (-2)(-4) = 8 and (-2) + (-4) = -6. Rewriting gives (x - 2)(x - 4) = 0, so x = 2 or x = 4. The roots are 2 and 4. Other options don’t multiply to 8 or don’t sum to -6, so they don’t solve the equation.