## anonymous one year ago Marvin was completing the square, and his work is shown below. Identify the line where he made his mistake. f(x) = 2x^2 − 8x + 5 Line 1: f(x) = 2(x^2 − 8x) + 5 Line 2: f(x) = 2(x^2 − 8x + 16) + 5 − 32 Line 3: f(x) = 2(x − 4)^2 − 27 Line 1 Line 2 Line 3 He did not make any mistakes I think line 2, amirite?

1. anonymous

yes, he didn't factor the 2 out correctly

2. dinamix

f(x) =2x^2-16x+5 this equation i think the answer is line 3

3. anonymous

oh wait, sorry. That factoring mistake is on line 1, not 2.

4. dinamix

yup this @peachpi and he didnt right the correct must will f(x) = 2x^2-16x+5 and the aswer line 3

5. dinamix

2(x^2-4) @peachpi

6. anonymous

Y'all lost me

7. anonymous

\(2x^2-8x\) = \(2(x^2-4x)\) is what I meant

8. anonymous

they're asking you to find the mistake. The mistake is that the factoring on line 1 was wrong.

9. dinamix

all lines is wrong @peachpi

10. anonymous

yes, they're all wrong. But the mistake first happened on line 1

11. anonymous

Oh, alright, I see where you guys are coming from

12. dinamix

i think he made mistake in f(x) = 2x^2-8x+5 and should be 2x^2-16x+5 peachpi

13. dinamix

and the lines will be all correct

14. dinamix

did understand me @peachpi

15. anonymous

No. I don't know where you're getting that. The two expressions you typed aren't equal. This problem is about completing the square, which is basically rewriting the same thing in another way. You can't just change -8x to -16x because it changes the value of the expression.

16. dinamix

yup he did write it correct thats problem

17. dinamix

u didnt understand me if the function f(x) = 2x^2-16x+5 we all lines correct right ?

18. dinamix

find*

19. anonymous

No, because changing -8 to -16 changes the function. This is the correct solution to the problem, with no mistakes \(f(x)=2x^2-8x+5\) \(f(x)=2(x^2-4x)+5\) \(f(x)=2(x^2-4x+4)+5-8\) \(f(x)=2(x-2)^2-3\)

20. anonymous

Is he getting confused with the actual function? Hes really confusing me

21. anonymous

yeah I think so. If you compare what I have with the solution in the problem statement, you can see the mistake on the first line

22. anonymous

He didn't divide the 8x by the 2 you're factoring?

23. dinamix

@gigirained are really this function f(x) = 2x^2-8x+5 are u sure its -8x not -16x ?

24. anonymous

yes correct @gigirained

25. anonymous

Positive its -8x

26. anonymous

@dinamix I see what you're doing. The objective of the problem is to find the mistake, if there is one. You're finding a function that matches the steps provided. So yeah if the initial function had -16x, then the work would be correct.

27. dinamix

ok he did mistake , didnt divide 8x by 2

28. dinamix

yup @peachpi this why i check if write function correct or no

29. anonymous

Thanks you guys, @peachpi and @dinamix