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# Quick completing the square q watch

1. Say there was an ordinary question about competing the square with x^2 at the front, you'd have the first 2 terms so the x^2 and the second x term. When you put those 2 terms into a bracket, would the x on the second term stay there or woud you get rid of it?

Like this:

(x-3x)^2 - 4
or (x-3) - 4

Would the x stay in the bracket or be removed?
2. (Original post by Magenta96)
Say there was an ordinary question about competing the square with x^2 at the front, you'd have the first 2 terms so the x^2 and the second x term. When you put those 2 terms into a bracket, would the x on the second term stay there or woud you get rid of it?

Like this:

(x-3x)^2 - 4
or (x-3) - 4

Would the x stay in the bracket or be removed?
You'd get rid of the x, but it's (x-3)^2 - 4 not (x-3) - 4.
3. (Original post by Magenta96)
Say there was an ordinary question about competing the square with x^2 at the front, you'd have the first 2 terms so the x^2 and the second x term. When you put those 2 terms into a bracket, would the x on the second term stay there or woud you get rid of it?

Like this:

(x-3x)^2 - 4
or (x-3) - 4

Would the x stay in the bracket or be removed?
Your wording is confusing but the second x wouldn't be there.
For example for (x-2)^2-8
X^2-6x-4
(X-3)^2 -9 -4
So (X-3)^2 -13
4. (Original post by HenryD)
Your wording is confusing but the second x wouldn't be there.
For example for (x-2)^2-8
X^2-6x-4
(X-3)^2 -6 -4
So (X-3)^2 -10

There is a mistake here.

The minus 6 should be minus 9
5. (Original post by Magenta96)
Say there was an ordinary question about competing the square with x^2 at the front, you'd have the first 2 terms so the x^2 and the second x term. When you put those 2 terms into a bracket, would the x on the second term stay there or woud you get rid of it?

Like this:

(x-3x)^2 - 4
or (x-3) - 4

Would the x stay in the bracket or be removed?

Neither of these are correct.

Complete the square for

x^2 -6x -1

Then x^2 -6x -1 = (x - 3)^2 - 3^2 -1= (x - 3)^2 - 10
6. (Original post by Magenta96)
Say there was an ordinary question about competing the square with x^2 at the front, you'd have the first 2 terms so the x^2 and the second x term. When you put those 2 terms into a bracket, would the x on the second term stay there or woud you get rid of it?

Like this:

(x-3x)^2 - 4
or (x-3) - 4

Would the x stay in the bracket or be removed?
Do you understand why Completing the Square works

Do you know what the expansion of (x-3x)^2 is and what the expansion of (x-3)^2 is and why the second one is relevant to your question?
7. (Original post by steve2005)
There is a mistake here.

The minus 6 should be minus 9
You're right, thanks for the correction.
8. (Original post by HenryD)
Your wording is confusing but the second x wouldn't be there.
For example for (x-2)^2-8
X^2-6x-4
(X-3)^2 -9 -4
So (X-3)^2 -13
Oh right yes, I know the method for completing the square, I was just wondering about the bolded bit. I always got confused if the x stayed in or was removed.

Thanks
9. Thanks, the equations in my question were just random examples I made up to demonstrate my point, I understand now that the x doesn't stay in the brackets. Thanks

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