SAT Math Multiple Choice Question 272: Answer and Explanation
2. If x2 – 8x = 48 and x < 0, what is the value of x + 10?
- A. –2
- B. 4
- C. 6
- D. 8
Correct Answer: C
Category: Passport to Advanced Math / Quadratics
Strategic Advice: There are a number of ways to solve quadratic equations. When the coefficient of x2 is 1, the quickest way is usually to factor, if possible. You could also use the quadratic formula or completing the square.
Getting to the Answer: To answer this question, first rewrite the equation in standard form, x2 - 8x - 48 = 0, and then factor to arrive at (x - 12)(x + 4) = 0. Using the Zero-Product property to solve for x results in x = 12 and x = -4. It is given that x < 0, so x must equal -4. This means that x + 10 is equal to -4 + 10 = 6.