Question

Find the quadratic function that has a vertex at (3,4) and goes through the point (0,13).​

Answer 1

Answer:

f

(

x

)

=

−

1

2

x

2

+

3

x

−

1

2

Explanation:

A quadratic function can be written in vertex form as:

f

(

x

)

=

a

(

x

−

h

)

2

+

k

where

(

h

,

k

)

is the vertex and

a

is a constant multiplier.

In our example the vertex

(

h

,

k

)

is

(

3

,

4

)

, so we can write:

f

(

x

)

=

a

(

x

−

3

)

2

+

4

Given that this passes through the point

(

1

,

2

)

, we must have:

2

=

a

(

1

−

3

)

2

+

4

=

4

a

+

4

Subtract

4

from both ends to get:

−

2

=

4

a

Divide both sides by

4

and transpose to find:

a

=

−

1

2

So our quadratic function can be written in vertex form as:

f

(

x

)

=

−

1

2

(

x

−

3

)

2

+

4

We can multiply this out and simplify as follows:

f

(

x

)

=

−

1

2

(

x

−

3

)

2

+

4

f

(

x

)

=

−

1

2

(

x

2

−

6

x

+

9

)

+

4

f

(

x

)

=

−

1

2

x

2

+

3

x

−

9

2

+

4

f

(

x

)

=

−

1

2

x

2

+

3

x

−

1

2

Step-by-step explanation:

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