Question

−2x=x2−6 Rewrite the equation by completing the square.

Answer 1

Answer:

(x + 1)² = 7

Step-by-step explanation:

Given:

-2x = x² - 6

We'll start by rearranging it to solve for zero:

x² + 2x - 6 = 0

The first term is already a perfect square so that's fine.  Normally, if that term had a non-square coefficient, you would need to multiply all terms a value that would change that constant to a perfect square.

Because it's already square (1), we can simply move to the next step, separating the -6 into a value that can be doubled to give us the 2, the coefficient of the second term.  That value will of course be 1, giving us:

x² + 2x + 1 - 1 - 6 = 0

Now can group our perfect square on the left and our constants on the right:

x² + 2x + 1 - 7= 0

x² + 2x + 1 = 7

(x + 1)² = 7

To check our answer, we can solve for x:

x + 1 = ± √7

x = -1 ± √7

x ≈ 1.65, -3.65

Let's try one of those in the original equation:

-2x = x² - 6

-2(1.65) = 1.65² - 6

- 3.3 = 2.72 - 6

-3.3 = -3.28

Good.  Given our rounding that difference of 2/100 is acceptable, so the answer is correct.