Completing the square follows the principle of taking

and converting it into

where d is the 'correctional number' as I like to call it - i.e. the number that converts the expanded bracket into the +c, since the expanded bracket will give us

.
In this case, 2/2=1 so we have the first part:

.
Expanding this gives us

. We need c to be 9, so we can just add 8.
Putting this together:

Now we can solve it more easily.
Rearranging:
Three real world examples of rectangular prisms include juice boxes, cereal boxes, and even cargo containers. Two real world examples of triangular prisms include camping tents and triangular roofs. I chose these objects to represent triangular and rectangular prisms because triangular prisms have two triangular faces and three rectangular faces and rectangular prisms have six rectangular faces.
Sample Response: Boxes, ice cubes, and brick are examples of rectangular prisms. Ramps and tents are examples of triangular prisms. A rectangular prism has six rectangular faces. A triangular prism has two triangular faces and three rectangular faces.
Answer:
(x - 4) to the second power
Step-by-step explanation: