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Maths GCSE help please!! - completing the square.

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.

Reply 1

selugawi

I don't think your answers are right, did your teacher give them to you?

Reply 2

harlz_chalamet

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

Reply 3

username5794123

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?

Reply 4

harlz_chalamet

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.

Reply 5

username5794123

Original post by harlz_chalamet

I got the same answer for the first one. What did you do for the second question as it seems a bit off?

(edited 2 years ago)

Reply 6

harlz_chalamet

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 :smile:

Reply 7

harlz_chalamet

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!

completing the square question!.docx19.5KB

Reply 8

username5794123

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.

Reply 9

mqb2766

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