How to sketch the graph of a parabola centered at (h, k), given a standard form equation.
1. Determine which of the standard forms applies to the given equation:
(y − k)
2
= 4p (x − h) or (x−h)
2
=4p(y−k).
2. Use the standard form identified in Step 1 to determine the vertex, axis of symmetry,
focus, equation of the directrix, and endpoints of the latus rectum.
1. If the equation is in the form (y − k)
2
= 4p (x − h), then:
-use the given equation to identify h and k for the vertex, (h, k)
-use the value of k to determine the axis of symmetry, y = k
-set 4p equal to the coefficient of (x − h) in the given equation to solve for p. If p > 0,
the parabola opens right. If p < 0, the parabola opens left.
-use h, k, and p to find the coordinates of the focus, (h + p, k)
-use h and p to find the equation of the directrix, x = h − p
-use h, k, and p to find the endpoints of the latus rectum, (h + p, k ± 2p)
2. If the equation is in the form (x − h)
2
= 4p (y − k), then:
-use the given equation to identify h and k for the vertex, (h, k)
-use the value of h to determine the axis of symmetry, x = h
-set 4p equal to the coefficient of (y − k) in the given equation to solve for p. If p > 0,
the parabola opens up. If p < 0, the parabola opens down.
-use h, k, and p to find the coordinates of the focus, (h, k + p)
-use k and p to find the equation of the directrix, y = k − p
-use h, k, and p to find the endpoints of the latus rectum, (h ± 2p, k + p)
3. Plot the vertex, axis of symmetry, focus, directrix, and latus rectum, and draw a smooth
curve to form the parabola.