Question

I think of a number.

If I subtract 20 from my number, then square the result,
I get the same answer as
if I square my number, then subtract 20 from the result.
What is my number?
You must show an algebraic method (use letter x in your working).

Answer 1

10.5

Explanation:

(X - 20)² = (X)² - 20

(X - 20)(X- 20) = X² - 20

X² - 20X - 20X + 400 = X² - 20

X² - 40X + 400 = X² - 20

X² - X² - 40X = -20 - 400

-40X = -420

X = -420/-40

X = 10.5