# Why is (x+3) the correct factor of x^2- 3x- 18?

Please explain.

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- Anonymous9 years agoFavourite answer
That is because of the factoring decomposition!

By factoring decomposition, determine two values in which the product is -18 and the sum is -3. They are -6 and +3, so rewrite the expression as...

x² - 6x + 3x - 18

Use grouping to get...

x(x - 6) + 3(x - 6)

= (x - 6)(x + 3)

Good luck!

Source(s): σ_σ - Anonymous9 years ago
Put -3 into the equation, it equals 0, therefore it is a factor of the equation.

Also:

(x+3)(x-6)=x^2- 3x- 18

- MechEng2030Lv 79 years ago
x^2 - 3x - 18 itself factors into (x + 3)(x - 6)... So obviously (x + 3) is going to be a factor

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