Question

Which equation is a solution to (x-3)(x+9)=27?

Answer 1

Answer:

x = ± $3\sqrt{7}$ - 3

Explanation:

I'm assuming you want the solutions to that equation, so here goes! (If not, please comment.)

(x-3)(x+9)=27

Let's FOIL this all out and expand. (Remember: First, Outer, Inner, Last.)

x^2 +   9x    -    3x    -  27

(first+ inner + outer + last)

x^2 + 9x - 3x - 27 = 27

Combine like terms, and add 27 to both sides.

x^2 + 6x - 27 + 27 = 27 + 27

x^2 + 6x = 54

Let's complete the square, because factoring doesn't work, and because it's good practice.

x^2 + 6x + ___ = 54 + ____

In the blank we will put b/2 ^2 = 6/2 ^2 = 3^2 = 9 to complete the square.

x^2 + 6x + 9 = 54 + 9

Now we've got a perfect square factor:

(x + 3)^2 = 63

sqrt(x+3)^2 = $\sqrt{63}$

x + 3 = ± $3\sqrt{7}$

x = ± $3\sqrt{7}$ - 3