Madeline was completing the square, and her work is shown below. Identify the line where she made her mistake.

f(x) = 3x2 + 6x − 7
Line 1: f(x) = 3(x2 + 2x) − 7
Line 2: f(x) = 3(x2 + 2x + 1) − 7 − 1
Line 3: f(x) = 3(x + 1)2 − 8

Line 1

Line 2

Line 3

She did not make any mistakes

Question

Madeline was completing the square, and her work is shown below. Identify the line where she made her mistake.

f(x) = 3x2 + 6x − 7
Line 1: f(x) = 3(x2 + 2x) − 7
Line 2: f(x) = 3(x2 + 2x + 1) − 7 − 1
Line 3: f(x) = 3(x + 1)2 − 8 

 Line 1

 Line 2

 Line 3

 She did not make any mistakes

anonymous · Answer

it can be a little tricky to read your x and your multiplying.

igreen · Answer

Line 2.

geekfromthefutur · Answer

can u explain y iGreen

igreen · Answer

I graphed all three, only Line 1 is exactly the same as $f(x) = 3x^2 + 6x - 7$. Line 2 and 3 are exactly the same, but are NOT exactly the same as $f(x) = 3x^2 + 6x - 7$.

igreen · Answer

Graphing Site: https://www.desmos.com/calculator

anonymous · Answer

oooh! haha completing the square, i should have known what geek was trying to say

igreen · Answer

I hate completing the square, I never learned it..'cause it was too confusing..

geekfromthefutur · Answer

lol ik how u feel my teacher just gave me a test and we haven't even studied for it yet or talked about it

anonymous · Answer

The problem lies here.
 3(x2 + 2x + 1)
where is this +1 coming from?
also,  where is this -1 coming from?
-7 − 1

igreen · Answer

Welp, that's how I got the answer. Do you understand? @geekfromthefutur