Expand the left side:

(n – 5)(n – 5) = 20

n^2 – 10n + 25 = 20

Now, set the equation equal to zero:

n^2 – 10n + 25 = 20

n^2 – 10n + 5 = 0

To solve for n, you’ll have to use the quadratic formula:

n^2 – 10n + 5 = 0

[-b ± sqrt(b^2 – 4ac)] / 2a

Where a = 1, b = -10, c = 5

n = 5 – 2*sqrt(5) = 0.527864

n = 5 + 2*sqrt(5) = 9.47214

Good luck in your studies,

~ Mitch ~

P.S. – Ichweissallez’s answer is the easiest to understand.

(n-5)(n-5) = 20

Use FOIL (first, outside, inside, last)

Solve for N

the guy’s answer after mine makes a LOT more sense — taking the square root of each side

and once done, it should look like

When you put something in a sqrt you must make it [+/-]

(n-5)=[+/-]sqrt20

SIMPLIFY THE ROUTE

(n-5)=[+/-]2sqrt5

ADD 5 TO BOTH SIDES

n=5[+/-]2sqrt5**

**edit when i did my last step I didn’t copy correctly

people below me can’t leave 20 in a sqrt because it’s not simplified (2sqrt5 is more acceptable than sqrt20)