Solving Quadratic Equations: Completing the Square (Continued) — Quiz

Question 6 • Algebra I

Inga is solving 2 x squared plus 12 x minus 3 is equal to 0 Which steps could she use to solve the quadratic equation? Choose three correct answers.

Answer

x plus 3 is equal to plus or minus square root of 21 halves

2 times open paren x squared plus 6 x close paren is equal to negative 3

2 times open paren x squared plus 6 x close paren is equal to 3

2 times open paren x squared plus 6 x plus 9 close paren is equal to 3 plus 18

2 times open paren x squared plus 6 x plus 9 close paren is equal to negative 3 plus 9

Explanation

Move the constant term to the right: 2x² + 12x = 3, or 2(x² + 6x) = 3, which is choice C. Complete the square by adding 9 inside the parentheses; because the expression is multiplied by 2, this adds 18, giving 2(x² + 6x + 9) = 3 + 18, choice D. Then 2(x + 3)² = 21, so x + 3 = ±√(21/2), choice A.

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