Completing the Square for y = 3x² - 12x + 7

[Darmok]

Completing the Square for y = 3x² - 12x + 7

Hello, I did this question from my homework and got it slightly wrong. I checked it over multiple times but still don't know what I screwed up.

Question y=3x² -12x + 7 Complete the Square

Here is what I did:

I used the formula -b/2a to figure out what x is. Here -b/2a is -1x-12/2x3 which is 12/6. 12÷6=2 so x=2. Then I plugged it in.

y=3(2)² -12(2) + 7

y=12 -24 +7

y=-5

Now that I had x and y I put it into vertex form, how the answers are supposed to appear.

y= 3(x-2)²-5 My final answer.

The answer in the book was y= 3(x-2)²+3

What did I do wrong?

 

[mmm4444bot]

You can confirm that the book's answer is wrong, by multiplying it out and simplifying. :cool:

 

[Bob Brown MSEE]

Or just test at x=0

Problem:
y=3x² -12x + 7
check y(0)
y(0) = 3(0)²-12(0)+7
y(0) = 7

The answer in the book was:
y= 3(x-2)²+3
check y(0)
y(0) = 3(0-2)²+3
y(0) = 3(4)+3
y(0) = 3(4)+3
y(0) = 15 WRONG should be 7