Completing the square and finding x

Alltimesarah

2

Hey tsr
Is this right so far, just spent an hour on this topic and I still can't confidently find the x terms :frown:

the original question is 2x^2 + 8x - 10 :smile:

Thanks

ImageUploadedByStudent Room1381265490.673749.jpg

Posted from TSR Mobile

(edited 10 years ago)

Reply 1

user2020user

16

Original post by Alltimesarah

Hey tsr
Is this right so far, just spent an hour on this topic and I still can't confidently find the x terms :frown:

Thanks

Posted from TSR Mobile

Could you type the question in full? It's hard to see what you want to do from your working.

Reply 2

Cammy150

1

sorry this sprung to mind. May have different working

Reply 3

Cammy150

1

Original post by Cammy150

sorry this sprung to mind. May have different working

to add to this.

(2x + 10) = 0
2x = -10
x =-5

also

(x-1) = 0
x = 1

Reply 4

Alltimesarah

OP

2

Original post by Khallil

Could you type the question in full? It's hard to see what you want to do from your working.

Sorry, it's my bad phone camera! Oops

2(x^2+4x) - 10
My final answer was (x+2)^2 -28 :smile:

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Reply 5

Alltimesarah

OP

2

Original post by Cammy150

sorry this sprung to mind. May have different working

Thank you! But how did you get
2x + 10 = 10x :smile:

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Reply 6

Kilaskwiral

10

Cammy, what you've done is factorising, not completing the square.

I refer you to THE COMPLETING THE SQUARE SONG (to the tune of Winnie the Pooh)

Completing the square, completing the square,
Halve the x and put in brackets
Subtract the square, of that number there
We have completed the square!

#FURTHERMATHSANTHEM

Reply 7

Cynical-

2((x+2)^2-4)-10
2(x+2)^2-8-10
2(x+2)^2-18

Would also be useful if you could give us the starting question.
You cannot equate completing squares to 0.

(edited 10 years ago)

Reply 8

user2020user

16

Original post by Alltimesarah

Sorry, it's my bad phone camera! Oops

2(x^2+4x) - 10
My final answer was (x+2)^2 -28 :smile:

Posted from TSR Mobile

No no. What I mean is, can you type the question as it is given in the book/pdf/whatever you may be viewing?

I have no idea what you're trying to do. I know you're completing the square, but I don't know what equation you were told to factorise to begin with, nor do I know if you're required to find the roots, minimum point etc.

(edited 10 years ago)

Reply 9

Alltimesarah

OP

2

I am such an idiot sorry everyone the question is
2x^2 + 8x -10

I'll just edit my first post now :smile:

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Reply 10

user2020user

16

Original post by Alltimesarah

I am such an idiot sorry everyone the question is
2x^2 + 8x -10

I'll just edit my first post now :smile:

Surely the question can't just be:

i) \ 2x^2 + 8x - 10

How are you supposed to know what to do with the quadratic? :s-smilie:

Reply 11

Alltimesarah

OP

2

Original post by Khallil

Surely the question can't just be:

i) \ 2x^2 + 8x - 10

How are you supposed to know what to do with the quadratic? :s-smilie:

My teacher just said complete the square and try to find x (if that makes sense ahaa)

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Reply 12

Cynical-

Original post by Khallil

Surely the question can't just be:

i) \ 2x^2 + 8x - 10

How are you supposed to know what to do with the quadratic? :s-smilie:

Ignore the -10, take out a factor of 2 from the first two numbers and complete the square then expand brackets, takeaway the integers and wala, I refer you to post 8

(edited 10 years ago)

Reply 13

user2020user

16

Original post by Cynical-

Ignore the -10, take out a factor of 2 from the first two numbers and complete the square then expand brackets, I refer you to post 8

I'm fully aware of how to complete the square on a quadratic. I was asking what the OP was meant to do once they had completed the square. You can do a number of things once it has been factorised, which is why I was asking if there was anything specific. The OP replied with "the teacher told them to complete the square and find x" so I can only assume the teachers wants the OP to find the roots of the quadratic equation.

(I've finished A Level maths and further maths)

(edited 10 years ago)

Reply 14

Alltimesarah

OP

2

Original post by Cynical-

Ignore the -10, take out a factor of 2 from the first two numbers and complete the square then expand brackets, takeaway the integers and wala, I refer you to post 8

Thank you! But where did the -8 come from? :s-smilie:

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Reply 15

Cynical-

Original post by Khallil

I'm fully aware of how to complete the square on a quadratic. I was asking what the OP was meant to do once they had completed the square. You can do a number of things once it has been factorised, which is why I was asking if there was anything specific. The OP replied with "the teacher told them to complete the square and find x" so I can only assume the teachers wants the OP to find the roots of the quadratic equation.

(I've finished A Level maths and further maths)