We are given the quadratic function:

The vertex form is given by:

So we have to convert our quadratic form into this vertex form.
We can do so by applying factoring by completing the square method.

Step 1:
We take half of coefficient of x and add it to x.
Coefficient of x is 14, half of it is 7.
(x+7)²
Step 2:
Subtract square of 7 that is 49,
(x+7)²-49+40
(x+7)²-9
Answer:
The vertex form is given by:
