Math question, distributive property dealing w/ quadratic form.

Question

So right now im dealing with changing vertex form of a quadratic equation and turning it into standard form. Vertex form is (x-2)^2-9. She put it in binomial form which I understand but when she did distributive property she got x^2-2x-2x+4-9. Where did the 4 come from?

Answer 1

(a - b) * (a - b) = a² + a * (-b) + (-b) * (a) +

(-b) * (-b)

(x - 2) * (x - 2) = x² + x * (-2) + (-2) * x + (-2) * (-2) = x² - 2x - 2x + 4.

So, 4 came from (-2) * (-2).

If you stuck, lost or in hurry because of the test, use a simple rule, replace "-" by +, but correctly of cause. Here:

(X - 2)²= (X + (-2))²

Now you have ( A + B) ², where B just happened to be a negative number.

Your teacher did just that, but did that in his/her mind, she didn't write (-2) * (-2), but write just 4, but this 4 came exactly from what I have described above.

This is a very simple thing, but when you missed things like this here and there, it became a big problem over a time.