# ALGEBRA 1

The square of a number is equal to the sum of 21 and 4 times the number. Find the number

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1. let the number be x

translate into math

x^2 = 21 + 4x

x^2 - 4x - 21 = 0
(x-7)(x+3) = 0
x = 7 or x = -3

the number is either 7 or -3

check:
if the number is 7
the square of the number is 49
21 plus 4(7) = 49 , yeahh!

if the number is -3
the square of the number is 9
21 + 4(-3) = 9, yeahhh!
Both numbers work.

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