if the square of a negative number is decreased by 18, the result of three times the number

Answer 1

The square of a negative number is positive.

Three times a negative number is a more negative number.

So, the number must be very close to zero.

-1 doesn't work because 1 - 18 = -17

-2 doesn't work because 4 - 18 = -14

-3 works because 9 - 18 = -9 which three times -3.

OR

x² - 18 = 3x where x is a negative number

x² - 3x - 18 = 0

x² - 3x = 18

x² - 3x + 9/4 = 18 + 9/4

(x - 3/2)² = 81/4

x - 3/2 = +/- 9/2

x = 12/2 or -6/2

x is negative, so x = -6/2, which is -3.