I rearranged an implicit differentiation equation wrong help. maths alevel june 2018

I think I lost 2 marks even though I was so close to the answer. I just multiplied my answer by -1 at the end but Im pretty sure thats incorrect maths Screenshot 2023-05-07 10.15.01 AM.png

(edited 11 months ago)

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Reply 1

Notnek

Original post by leoishush

I think I lost 2 marks even though I was so close to the answer. I just multiplied my answer by -1 at the end but Im pretty sure thats incorrect maths

Your answer is correct and is the same as the mark scheme.

(edited 11 months ago)

Reply 2

ghostwalker

Original post by leoishush

I think I lost 2 marks even though I was so close to the answer. I just multiplied my answer by -1 at the end but Im pretty sure thats incorrect maths Screenshot 2023-05-07 10.15.01 AM.png

You've multiplied the top and the bottom by "-1", which is the same thing as multplying the whole thing by "1". it's fine.

Reply 3

leoishush

ahhh thats great thanks @ghostwalker @Notnek

Reply 4

leoishush

CE719BF0-0523-4FD8-94D5-F02D02B85EC9.jpg.jpeg

. I can’t seem to find where I went wrong with this Intergration from the same paper as well Screenshot 2023-05-07 10.59.40 AM.png

(edited 11 months ago)

Reply 5

ghostwalker

Original post by leoishush

. I can’t seem to find where I went wrong with this Intergration from the same paper as well Screenshot 2023-05-07 10.59.40 AM.png

From your working

du = 1/(2u) dx

I.e. dx = 2u du.

Your replacing the dx in the integral, so that will become the 2u du, not 1/(2u) du.

Reply 6

leoishush

Original post by ghostwalker

From your working

du = 1/(2u) dx

I.e. dx = 2u du.

Your replacing the dx in the integral, so that will become the 2u du, not 1/(2u) du.

ugh I would of gotten the answer right. Thank you very much.

Reply 7

Coolbeanz247

Original post by leoishush

I think I lost 2 marks even though I was so close to the answer. I just multiplied my answer by -1 at the end but Im pretty sure thats incorrect maths Screenshot 2023-05-07 10.15.01 AM.png

The way to get the answer in the form that the question wants is to take the 2x to the RHS and take the 2x(dy/dx) to the LHS. Then do the same steps as u did and you will get (y-x)/(3y-x)