Answer:
First Box: Factor by difference of squares
Second Box: It has all perfect squares
Third Box: see my work
Step-by-step explanation:
We have the equation 
Before we do anything, let us bring all of the terms to the left side

Now that we have moved the terms to one side, it is clear that we have a difference of squares.
-Work-

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7^2x4 = n^8
7^8 = n^8
n = 7
Answer:
Step-by-step explanation:
Draw a picture!
You get a right triangle with hypotenuse = 20 ft and horizontal leg = 12 ft
Use the Pythagorean Theorem to find the length of the vertical leg:
vertical leg = √(20²-12²) = √256 = 16 ft
The expansion of a perfect square is

In words, the square of a sum of two terms is the sum of the squares of the two terms (
and
), plus twice the product of the two terms (
)
So, when determining if you have a perfect square trinomial, you should have two perfect squares. Note that they don't have to be the first and third term, since you can rearrange terms as you prefer.