# Graph y=x^2-4x-18 y=x2-4x-18
Find the properties of the given parabola.
Rewrite the equation in vertex form.
Complete the square for x2-4x-18.
Use the form ax2+bx+c, to find the values of a, b, and c.
a=1,b=-4,c=-18
Consider the vertex form of a parabola.
a(x+d)2+e
Substitute the values of a and b into the formula d=b2a.
d=-42(1)
Simplify the right side.
Cancel the common factor of 4 and 2.
Factor 2 out of 4.
d=-2⋅22⋅1
Cancel the common factors.
Factor 2 out of 2⋅1.
d=-2⋅22(1)
Cancel the common factor.
d=-2⋅22⋅1
Rewrite the expression.
d=-21
Divide 2 by 1.
d=-1⋅2
d=-1⋅2
d=-1⋅2
Multiply -1 by 2.
d=-2
d=-2
Find the value of e using the formula e=c-b24a.
Simplify each term.
Cancel the common factor of (-4)2 and 4.
Rewrite -4 as -1(4).
e=-18-(-1⋅4)24(1)
Apply the product rule to -1(4).
e=-18-(-1)2⋅424(1)
Raise -1 to the power of 2.
e=-18-1⋅424(1)
Multiply 42 by 1.
e=-18-424(1)
Factor 4 out of 42.
e=-18-4⋅44⋅1
Cancel the common factors.
Factor 4 out of 4⋅1.
e=-18-4⋅44(1)
Cancel the common factor.
e=-18-4⋅44⋅1
Rewrite the expression.
e=-18-41
Divide 4 by 1.
e=-18-1⋅4
e=-18-1⋅4
e=-18-1⋅4
Multiply -1 by 4.
e=-18-4
e=-18-4
Subtract 4 from -18.
e=-22
e=-22
Substitute the values of a, d, and e into the vertex form a(x+d)2+e.
(x-2)2-22
(x-2)2-22
Set y equal to the new right side.
y=(x-2)2-22
y=(x-2)2-22
Use the vertex form, y=a(x-h)2+k, to determine the values of a, h, and k.
a=1
h=2
k=-22
Since the value of a is positive, the parabola opens up.
Opens Up
Find the vertex (h,k).
(2,-22)
Find p, the distance from the vertex to the focus.
Find the distance from the vertex to a focus of the parabola by using the following formula.
14a
Substitute the value of a into the formula.
14⋅1
Cancel the common factor of 1.
Cancel the common factor.
14⋅1
Rewrite the expression.
14
14
14
Find the focus.
The focus of a parabola can be found by adding p to the y-coordinate k if the parabola opens up or down.
(h,k+p)
Substitute the known values of h, p, and k into the formula and simplify.
(2,-874)
(2,-874)
Find the axis of symmetry by finding the line that passes through the vertex and the focus.
x=2
Find the directrix.
The directrix of a parabola is the horizontal line found by subtracting p from the y-coordinate k of the vertex if the parabola opens up or down.
y=k-p
Substitute the known values of p and k into the formula and simplify.
y=-894
y=-894
Use the properties of the parabola to analyze and graph the parabola.
Direction: Opens Up
Vertex: (2,-22)
Focus: (2,-874)
Axis of Symmetry: x=2
Directrix: y=-894
Direction: Opens Up
Vertex: (2,-22)
Focus: (2,-874)
Axis of Symmetry: x=2
Directrix: y=-894
Select a few x values, and plug them into the equation to find the corresponding y values. The x values should be selected around the vertex.
Replace the variable x with 1 in the expression.
f(1)=(1)2-4⋅1-18
Simplify the result.
Simplify each term.
One to any power is one.
f(1)=1-4⋅1-18
Multiply -4 by 1.
f(1)=1-4-18
f(1)=1-4-18
Simplify by subtracting numbers.
Subtract 4 from 1.
f(1)=-3-18
Subtract 18 from -3.
f(1)=-21
f(1)=-21
-21
-21
The y value at x=1 is -21.
y=-21
Replace the variable x with 0 in the expression.
f(0)=(0)2-4⋅0-18
Simplify the result.
Simplify each term.
Raising 0 to any positive power yields 0.
f(0)=0-4⋅0-18
Multiply -4 by 0.
f(0)=0+0-18
f(0)=0+0-18
f(0)=0-18
Subtract 18 from 0.
f(0)=-18
f(0)=-18
-18
-18
The y value at x=0 is -18.
y=-18
Replace the variable x with 3 in the expression.
f(3)=(3)2-4⋅3-18
Simplify the result.
Simplify each term.
Raise 3 to the power of 2.
f(3)=9-4⋅3-18
Multiply -4 by 3.
f(3)=9-12-18
f(3)=9-12-18
Simplify by subtracting numbers.
Subtract 12 from 9.
f(3)=-3-18
Subtract 18 from -3.
f(3)=-21
f(3)=-21
-21
-21
The y value at x=3 is -21.
y=-21
Replace the variable x with 4 in the expression.
f(4)=(4)2-4⋅4-18
Simplify the result.
Simplify each term.
Raise 4 to the power of 2.
f(4)=16-4⋅4-18
Multiply -4 by 4.
f(4)=16-16-18
f(4)=16-16-18
Simplify by subtracting numbers.
Subtract 16 from 16.
f(4)=0-18
Subtract 18 from 0.
f(4)=-18
f(4)=-18
-18
-18
The y value at x=4 is -18.
y=-18
Graph the parabola using its properties and the selected points.
xy0-181-212-223-214-18
xy0-181-212-223-214-18
Graph the parabola using its properties and the selected points.
Direction: Opens Up
Vertex: (2,-22)
Focus: (2,-874)
Axis of Symmetry: x=2
Directrix: y=-894
xy0-181-212-223-214-18
Graph y=x^2-4x-18     