 The figure shows a parabola opening to the **right** with vertex at the origin and axis along the $x$-axis. Its standard equation is:
A$y^2 = 4ax$
B$y^2 = -4ax$
C$x^2 = 4ay$
D$x^2 = -4ay$
Answer & Solution
Correct answer: A. $y^2 = 4ax$
Memorize the four canonical forms (with $a > 0$):
| Equation | Opens |
|---|---|
| $y^2 = +4ax$ | right |
| $y^2 = -4ax$ | left |
| $x^2 = +4ay$ | upward |
| $x^2 = -4ay$ | downward |
A right-opening parabola has $y^2 = 4ax$ — option A.
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