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

$$3{x}^{2}+6x-7$$ fits the formula a{x}^{2}+bx+c, where a = 3, b = 6 and c = -7. Use the complete the square formula. 
$${a(x+D)}^{2}+E$$

 $$D=\frac{b}{2a}$$

Also, find E. $$E=c-\frac{{b}^{2}}{4a}$$

Plug in D and E in $${a(x+D)}^{2}+E$$ to receive your answer.

Hint: so Madeline got E wrong.

anonymous · Answer

Thanks

precal · Answer

Line two is wrong  
Madeline needs to -3(1)