Tricky Differentiation Question GCSE FURTHER MATHEMATICS

Hello! I do ccea further maths, in northern ireland ...so im in year 12 here, but it's the equivalent of year 11 in England...moving on from the blabber..

I have a maths mock on this thursday and it's everything we have covered in pure maths excluding logs(we havent finished it yet). So i was doing one of the old 'Additional Mathematics papers for pure Maths(PAPER 1) of May/June 2005 by CCEA.

I came across this deadly question, can anyone help me out please? Mock on thursday.

I can't find the mark scheme anywhere on the interweb and can you tell me whereabouts i went wrong please because i only got up to the differentiation part and got dy/dx= 2ax-5, with b=-1, i don't know what a=...c=4. It's mainly just part (i) that i got stuck on, which prevented me from doing the rest of the question! Please help! I have posted this exact thread on the Maths Exams forum.

I have attached the question http://www.thestudentroom.co.uk/attachment.php?attachmentid=481431

Thank you

RevisionLad

Hello! I do ccea further maths, in northern ireland ...so im in year 12 here, but it's the equivalent of year 11 in England...moving on from the blabber..

I have a maths mock on this thursday and it's everything we have covered in pure maths excluding logs(we havent finished it yet). So i was doing one of the old 'Additional Mathematics papers for pure Maths(PAPER 1) of May/June 2005 by CCEA.

I came across this deadly question, can anyone help me out please? Mock on thursday.

I can't find the mark scheme anywhere on the interweb and can you tell me whereabouts i went wrong please because i only got up to the differentiation part and got dy/dx= 2ax-5, with b=-1, i don't know what a=...c=4. It's mainly just part (i) that i got stuck on, which prevented me from doing the rest of the question! Please help! I have posted this exact thread on the Maths Exams forum.

I have attached the question http://www.thestudentroom.co.uk/attachment.php?attachmentid=481431

Thank you

RevisionLad

Hi This is an interesting question. You've correctly stated that dy/dx is in fact -5 when x = 0. This means that the x value returns 0, and since the form of a quadratic derivative is 2ax+b, then ax = 0 when x is 0, therefore meaning b is -5. So B is -5.
You have also said that when the curve crosses the the x axis the y value is 0. This means that when the curve crosses at (1,0), x = 1 when y = 0.
This can then be solved from here, a(1)^2 - 5*1+c = 0. where c is the y intercept (4).
The rest is basic quadratic maths. If you need further help let me know!!