SAT Math Multiple Choice Question 687: Answer and Explanation
A portion of the graph of the quadratic function y = f(x) is shown in the xy-plane above. The function g is defined by the equation g(x) = f(x) + b. If the equation g(x) = 0 has exactly one solution, what is the value of b?
- A. -2
- B. -1
- C. 1
- D. 2
Correct Answer: D
Advanced Mathematics (transformations) HARD
The graph of y = g(x) = f(x) + b is the graph of f vertically shifted up by b units. If g(x) = 0 has exactly one solution, the graph of y = g(x) can touch the x-axis at only one point: the vertex. Since the vertex of f has a y-coordinate of -2, this can only happen if f is shifted up 2 units, so b = 2.