SAT Math Multiple Choice Practice Question 401: Answer and Explanation
5. Let the function f be defined such that f(x) = x2 - c, where c is a constant. If f(-2) = 6, what is the value of c ?
Correct Answer: B
B Start by plugging in what you know into the function given. If f(x) = x2 – c, and f(–2) = 6, then plug in –2 for x in the function: f(–2) = (–2)2 – c. Solve and replace f(–2) with 6: 6 = 4 – c; 2 = –c; and c = –2. If you picked answer choice A, you forgot that (–2)2 is positive 4, and if you picked answer choice E then you forgot about the minus sign in the original function.