Which of the following describes the graphs y = 3x and y = −3x correctly?

Question

A. These graphs are similar because they have the same y-intercept.
B. These graphs are similar because they both have positive slopes.
C. These graphs are similar because they both have negative slopes.
D. None of the above.

Answer 1

(A) is partially correct in that they both have the same y-intercept at (0,0), but that by itself does not make the graphs similar.  In fact, they are quite different, as one rises from left to right while the other falls from left to right, so (A) is not a good answer.  (B) and (C) are clearly false.  The best answer is none of the above, which is (D).