Question

Which of the following parabolas opens down?

Answer 1

ANSWER

The correct answer is C.

EXPLANATION

• The directrix of the parabolas are parallel to the x-axis.
• This means that, the orientation of the parabola is parallel to the y-axis.
• We compare the focus and the directrix to determine whether the parabola opens downwards or upwards.
• If the directrix is above the focus, then the parabola opens downwards.
• On the other hand if the directrix is below the focus , then the parabola must open upwards.
• If you look at option C, y=-2 isthe directrix. The focus is (3,-5). Since the the y-value of the focus , -5 is less than y=-2 which is the directrix, this parabola must open down.

The correct answer is C.