Problem:
A parabola has vertex at and has two -intercepts, one positive and one negative. If this parabola is the graph of , which of , and must be positive?
Answer Choices:
A. only
B. only
C. only
D. and only
E. none
Solution:
Because the parabola has -intercepts of opposite sign and the -coordinate of the vertex is negative, must be positive, and , which is the -intercept, must be negative. The vertex has -coordinate , so must be negative.