Maths GCSE help please!! - completing the square.

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harlz_chalamet
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#1
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#1
hi! i've asked my teacher for help, and she taught me how to do it but i'm still extremely stuck on this topic.

please may you go through these questions step by step?
it's solving quadratic, but you MUST use completing the square.


1) 2x^2 - 3x - 7= 0

the answer for that is:

x= -1 + root 6 OR x= -1 - root 6



2) 5x^2 + 2x - 8 = 0

the answer for this is:

x= -5 + root 37 OR x= -5 - root 37.


my teacher told me to work these out by always leaving the numbers in fractions. i've been doing this but i continuously kept on getting the answer wrong.
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selugawi
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#2
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#2
I don't think your answers are right, did your teacher give them to you?
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harlz_chalamet
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(Original post by selugawi)
I don't think your answers are right, did your teacher give them to you?
nooo those are the actual answers.
(the questions and answers are from corbettmaths).
i tried to find a video on how to do the question but there werent any
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username5794123
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(Original post by selugawi)
I don't think your answers are right, did your teacher give them to you?
I agree with this post. I don’t get the same answers as the OP. I even used my calculator afterwards to check and nope, the answers within the OP aren’t right.


@OP, what answers did you get?
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harlz_chalamet
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(Original post by 0ptics)
I agree with this post. I don’t get the same answers as the OP. I even used my calculator afterwards to check and nope, the answers within the OP aren’t right.


@OP, what answers did you get?
the answers i got were:

1) x= 3/4 + root 65/4 OR. x= 3/4 - root 65/4

2) x= -2/5 + root 41/5 OR x= -2/5 - root 41/5


i literally followed all of my teachers steps and did the question multiple times and i kept getting the same answer.
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username5794123
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#6
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(Original post by harlz_chalamet)
the answers i got were:

1) x= 3/4 + root 65/4 OR. x= 3/4 - root 65/4

2) x= -2/5 + root 41/5 OR x= -2/5 - root 41/5


i literally followed all of my teachers steps and did the question multiple times and i kept getting the same answer.
I got the same answer for the first one. What did you do for the second question as it seems a bit off?
Last edited by username5794123; 5 months ago
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harlz_chalamet
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(Original post by 0ptics)
I got the same answer for the first one. What did you do for the second question as it seems a bit off?
i'l try the second one again, and i'll post what i get. just give me a few mins.

thanks so much for your help
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harlz_chalamet
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(Original post by 0ptics)
I got the same answer for the first one. What did you do for the second question as it seems a bit off?
okay, hi. i may seem a bit extra but i wanted to type out the whole of my working out for the second question on word - so it would be easier to read.

here you go!
Attached files
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username5794123
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#9
(Original post by harlz_chalamet)
okay, hi. i may seem a bit extra but i wanted to type out the whole of my working out for the second question on word - so it would be easier to read.

here you go!
Sadly, I can’t see the file. It won’t let me open it.
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mqb2766
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#10
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#10
Apart from simplifying 2/10 to 1/5, the doc is fine.

Note if you're unsure, just check with the usual quadratic formula, you should get the same answer. In this case
-b/2a = -2/10 = -1/5
and
sqrt(b^2-4ac)/2a = sqrt(164)/10 = sqrt(41)/5
as in your doc
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harlz_chalamet
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(Original post by 0ptics)
Sadly, I can’t see the file. It won’t let me open it.
Name:  Screenshot 2021-12-12 at 17.57.38.png
Views: 7
Size:  72.5 KB are you able to see that? honestly, don't worry i you can't acess it - i could ask my teacher in a few days when i see her next
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username5794123
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#12
(Original post by harlz_chalamet)
Name:  Screenshot 2021-12-12 at 17.57.38.png
Views: 7
Size:  72.5 KB are you able to see that? honestly, don't worry i you can't acess it - i could ask my teacher in a few days when i see her next
That’s what I got. I was just confused because you said x = -2/5… and not x = -2/10…
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harlz_chalamet
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#13
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#13
(Original post by 0ptics)
That’s what I got. I was just confused because you said x = -2/5… and not x = -2/10…
ohhh right!
like u said earlier, i double checked by using the quadratic formula and it was right!! thank you so much for your help
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username5794123
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(Original post by harlz_chalamet)
ohhh right!
like u said earlier, i double checked by using the quadratic formula and it was right!! thank you so much for your help
No worries. Glad to see that you got the answers
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mqb2766
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#15
(Original post by harlz_chalamet)
ohhh right!
like u said earlier, i double checked by using the quadratic formula and it was right!! thank you so much for your help
This is fairly readable
https://www.mathsisfun.com/algebra/c...ng-square.html
and if you want to check quickly
https://www.wolframalpha.com/input/?...5E2%2B10x%2B28
comes in handy and solving
https://www.wolframalpha.com/input/?...0x+%2B+8+%3D+0
Last edited by mqb2766; 5 months ago
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