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# Factor completely 3x^{2} - 21.

3(x^{2} - 7), 3(x + 7)(x - 7), 3(x + 7)(x - 3), Prime

**Solution:**

Given: Expression is 3x^{2 }- 21

In order to find roots, we need to factor the polynomial.

⇒ 3x^{2} - 21

⇒ 3(x^{2} - 7)

This is in the form (a^{2} - b^{2}), we know that the difference of the squares (a^{2} - b^{2}) = (a + b)(a - b)

We can write (x^{2} - 7) as (x + 7) and (x - 7)

⇒ 3(x - 7)(x + 7)

Hence, by factoring completely, we get 3(x - 7)(x + 7).

## Factor completely 3x^{2} - 21.

**Summary:**

Factors of 3x^{2} - 21 are 3(x - 7)(x + 7).

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