Identify the vertex, focus, axis of symmetry, and directrix for the parabola
Spot the perfect-square trinomial instead of completing the square. The left side is already , because . Recognising this skips the completing-the-square step entirely:
Factor the right side so it looks like . Pull out :
The sign matters — writing instead would hide the value of .
Match to the horizontal template. Here is the squared variable, so the parabola opens sideways and the form is . Writing gives , and , so
Because the parabola opens left.
Locate the vertex and focus. The vertex is . For a horizontal parabola the focus is :
Give the axis and directrix. The axis of symmetry is the horizontal line through the vertex, . The directrix is the vertical line , three units to the right of the vertex — on the opposite side from the focus, as it must be.
Check one point against the definition. At the equation gives , so and lies on the curve. Its distance to the focus is , and its distance to the directrix is . The two distances agree.
Need to solve a different problem like this? Open the solver →