# How do I find the y-intercept of a parabola?

##### 1 Answer

**If given a graph:** the y-intercept passes through y-axis.

Example:

If a graph passes the y-axis at -1, then the y-intercept is -1.

If you can not see the y-axis, you need to chose two points and create the equation of the parabola in standard or vertex form (using vertex and another point).

Example on how to create an equation from the graph of the parabola (when y-axis cannot be seen):

Vertex: (3,4)

Point: (5, -4)

-4 =

-4 =

-4 =

-4 = 4a + 4

-4 - 4 = 4a

-8 = 4a

-2 = a

Equation: y =

**If an equation:** When a point is on the y-axis, the x value is 0. Therefore it you want to plug in 0 for your x values. y =

Example (vertex Form y =

y =

y =

y =

y = 3(16) +5

y = 48 + 5

y = 53

Y-intercept is 53

Example (Standard Form y =

y =

y =

y = 2(0) - 3(0) + 4

y = 0 - 0 + 4

y = 4 (the c value)

Y-intercept is 4