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# C1 maths Help watch

1. Could you please answer the question in steps,
question 6
and question 9 part (b)
Attached Images

2. (Original post by YesterdaysDreams)
Could you please answer the question in steps,
1) (a) By completing the square,
find in terms of the constant k the roots of the equation x2 + 4kx − k = 0
(b) Hence find the set of values of k for which the equation has no real roots.
What have you tried so far?
3. (Original post by SeanFM)
What have you tried so far?
I tried answering both questions
but i couldn't get the right answer
4. (Original post by YesterdaysDreams)
I tried answering both questions
but i couldn't get the right answer
Could you show us your working so we can show you where you went wrong or guide you through?
5. (Original post by YesterdaysDreams)
I tried answering both questions
but i couldn't get the right answer

What did you try? Please post your working if possible
6. (Original post by YesterdaysDreams)
Could you please answer the question in steps,
question 6
and question 9 part (b)
In part B you need to use the quadratic discriminant on x^2 + 4Kx - K, which is given by D = b^2 - 4ac.

The equation has no real roots if D < 0, so factorise the discriminant to get -2 +/- root(4K^2+K) < 0.

The equation has no real roots if root(4k^2 + K) < 0

Factorising therefore gives -1/4 < K < 0
Attached Images

7. (Original post by Dapperblook22)

Please find attached image

I am not sure if the second part is correct, I got K < 0, but check that against the answers and hope it helps
i get the first part (a)
but i still dont get part B
8. (Original post by SeanFM)

What did you try? Please post your working if possible
For question 6 i get part (a) not part (b)
(i don't think I'm able to screenshot my work, do i type it instead?)
9. (Original post by YesterdaysDreams)
For question 6 i get part (a) not part (b)
(i don't think I'm able to screenshot my work, do i type it instead?)
If your work is on your computer then you can screenshot it (or use the snipping tool if you have windows).

You can type it as long as it's clear what you're doing.
10. (Original post by Dapperblook22)

Please find attached image

I am not sure if the second part is correct, I got K < 0, but check that against the answers and hope it helps
umm i should be able to do these but i can't xD looks like some revision needs to be done but for part b doesn't the question mean the discriminant<0?

(Original post by YesterdaysDreams)
i get the first part (a)
but i still dont get part B
11. (Original post by Dapperblook22)

Please find attached image

I am not sure if the second part is correct, I got K < 0, but check that against the answers and hope it helps
(Original post by YesterdaysDreams)
i get the first part (a)
but i still dont get part B
Student403

shouldn't part b be

b²-4ac where b=4k a=1 and c=-k

so (4k)²-4*1*-k<0
16k²+4k<0
4k²+k<0
k(4k-1)<0
k<0 or k<0.25
12. (Original post by YesterdaysDreams)
For question 6 i get part (a) not part (b)
(i don't think I'm able to screenshot my work, do i type it instead?)
In part B you need to use the quadratic discriminant on x^2 + 4Kx - K, which is given by D = b^2 - 4ac.

The equation has no real roots if D < 0, so factorise the discriminant to get -2 +/- root(4K^2+K) < 0.

The equation has no real roots if root(4k^2 + K) < 0

Factorising therefore gives -1/4 < K < 0

(My first solution was only half right... but this is the actual answer)
13. (Original post by thefatone)
Student403

shouldn't part b be

b²-4ac where b=4k a=1 and c=-k

so (4k)²-4*1*-k<0
16k²+4k<0
4k²+k<0
k(4k-1)<0
k<0 or k<0.25
Yes it should, I just took a long way around in the first attempt :P
14. (Original post by Dapperblook22)
In part B you need to use the quadratic discriminant on x^2 + 4Kx - K, which is given by D = b^2 - 4ac.

The equation has no real roots if D < 0, so factorise the discriminant to get -2 +/- root(4K^2+K) < 0.

The equation has no real roots if root(4k^2 + K) < 0

Factorising therefore gives -1/4 < K < 0

(My first solution was only half right... but this is the actual answer)
isn't it supposed to be 0<k<0.25?
15. (Original post by thefatone)
Student403

shouldn't part b be

b²-4ac where b=4k a=1 and c=-k

so (4k)²-4*1*-k<0
16k²+4k<0
4k²+k<0
k(4k-1)<0
k<0 or k<0.25
Thanks
16. (Original post by thefatone)
isn't it supposed to be 0<k<0.25?
its -0.25
17. (Original post by YesterdaysDreams)
its -0.25
oh yea oops my mistake i found an error in my working xD
18. (Original post by thefatone)
isn't it supposed to be 0<k<0.25?
Definately -1/4 < k < 0, checked the mark scheme

https://a9497d7f220e174d38d014b2b1d8...%20Edexcel.pdf
19. (Original post by Dapperblook22)
Definately -1/4 < k < 0, checked the mark scheme

https://a9497d7f220e174d38d014b2b1d8...%20Edexcel.pdf
yup thanks
20. (Original post by YesterdaysDreams)
Could you please answer the question in steps,
question 6
and question 9 part (b)
Please find attached my working for part 9b, I am certain this one is right this time though because it is actually in the mark scheme and I checked it this time :P

EDIT: Oops, some of it was truncated. The answer at the end should be 2root7 as the length AB is found by subtracting the B value from the A value.

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