x = the number

(x + 3)² = 441 ← square of sum of number and 3 equals 441

(x + 3)(x + 3) = 441 ← squared binomial

x² + 6x + 9 = 441 ← foil method

x² + 6x - 432 = 0 ← subtracted 441

(x + 24)(x - 18) = 0 ← factored

x + 24 = 0 or x - 18 = 0 ← set to zero

x = -24 or x = 18 ← solved

The negative real number is -24

*McGenius*

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