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# Difficult C1 problem. Can anyone do this? watch

1. Hey guys I'm a bit stuck on this question.

Curve intersects at (-5, 0), (-2,0), (1.5, 0) and (0, -30)

i) Express the three points of intersection as an equation in fully factorised form.
which I put =(x+5)(x+2)(2x-3)
then it said
ii) Expand the brackets to show the equation of the curve can be written as 2x3 + 11x2 - x - 30. [2]
which I did.

Then it said: draw the line y =5x+2 accurately and find the x-coordinates of the points of intersection.
and so i made x = 0 and marked y as 2 and then made y = to get x= -2/5
I then read off the x-coordinates of intersection with the curve and i got -5.39 and 1.85

But I really don't understand how to do this next part...
it says:
Show that the x-coordinates satisfy the equation 2x2 +2x - 20=0.
Hence find the exact values of the x coordinates of the other points of intersection. [5]

How do I show that my values satisfy the equation? I got decimal numbers and I can't use a calculator.
I'm so confused.
2. Could you post the actually question?
3. (Original post by wednesday_adams)
Hey guys I'm a bit stuck on this question.
I was given a curve
So the first part of the problem says: draw the line y =5x+2 accurately and find the x-coordinates of the points of intersection.
and so i made x = 0 and marked y as 2 and then made y = to get x= -2/5
I then read off the x-coordinates of intersection with the curve and i got -5.39 and 1.85

But I really don't understand how to do this next part...
it says:
Show that the x-coordinates satisfy the equation 2x2 +2x - 20=0.
Hence find the exact values of the x coordinates of the other points of intersection. [5]

How do I show that my values satisfy the equation? I got decimal numbers and I can't use a calculator.
I'm so confused.
First you should put the two equations equal to each other, and re arrange them to get that equation
4. (Original post by jamez870)
Could you post the actually question?
I don't know how. It's on a sheet. :/
5. (Original post by wednesday_adams)
I don't know how. It's on a sheet. :/
Scan it or take a photo.
6. Also think about the quadratic formula.
7. (Original post by jamez870)
First you should put the two equations equal to each other, and re arrange them to get that equation

Ah!!! Thank you so much!!

so I've put the line equal to the curve and ended up with 2x^2 - 3x - 22 = 0

Because the question says find the 'exact' values of x I should use the quadratic formula, right?

(3+- sqrt 185)/4

this seems wrong as well

im stupid
8. (Original post by wednesday_adams)
Ah!!! Thank you so much!!

so I've put the line equal to the curve and ended up with 2x^2 - 3x - 22 = 0

Because the question says find the 'exact' values of x I should use the quadratic formula, right?

(3+- sqrt 185)/4

this seems wrong as well

im stupid
I think you have re arranged it incorrectly somewhere, you should end up with the equation they've put
9. (Original post by jamez870)
I think you have re arranged it incorrectly somewhere, you should end up with the equation they've put
I put 2x^2 + 2x - 20 = 5x + 2
2x^2 - 3x - 22 = 0
10. (Original post by wednesday_adams)
I put 2x^2 + 2x - 20 = 5x + 2
2x^2 - 3x - 22 = 0
I should have made the line = to the curve and not the equation

I should have put 5x+2 = 2x^3 +11x^2 - x - 30
and gotten 2x^3 + 11x^2 -6x - 32
..but then this is not a quadratic
11. (Original post by morgan8002)
Scan it or take a photo.
unfortunately i dont have a camera or a scanner..
But I have edited my post and written out the whole question now if that helps at all
12. (Original post by wednesday_adams)
I should have made the line = to the curve and not the equation

I should have put 5x+2 = 2x^3 +11x^2 - x - 30
and gotten 2x^3 + 11x^2 -6x - 32
..but then this is not a quadratic
I agree with that rearrangement, so either there's a misprint on your worksheet or there's some information missing that you haven't told us!

Can you check with your teacher that the worksheet is correct?

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