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Intergation problem

Im pretty confident with my integration and cant see anywhere ive gone wrong. could someone do this question and let me know what they get as im getting different to the answer but dont know how.

https://docs.google.com/document/d/e/2PACX-1vSwbevCNcF7043CNhizA98p2ASeiDf86c4f4t8tOWtb_79ObyIqRVMAE_O-aNfYcl23H5j8YRB9LvaU/pub
Can you post what you did / the given answer?
from a back of the envelope sketch it should be ~1?
(edited 1 year ago)
Original post by mqb2766
Can you post what you did / the given answer?
from a back of the envelope sketch it should be ~1?


its fine i got the answer in the end i went wrong by just a silly error. when integrating -24sin^3t i split it inot sin^2t and sint then used trig identity to get it to 1-cos^2(t) x sint and all i did worng from here was foregot to times by -1.

Your right it was just shy of 1 but the exact form i got it in was some nasty surd 16-(26/3)(root3)
Original post by mqb2766
Can you post what you did / the given answer?
from a back of the envelope sketch it should be ~1?


out of curiosity how did you find the area to be 1 by sketching?
Original post by charlie.R.12
out of curiosity how did you find the area to be 1 by sketching?


Its roughly a triangle of base 2 (beteen 4 and 6) and perp height 1.
Reply 5
Original post by charlie.R.12
its fine i got the answer in the end i went wrong by just a silly error. when integrating -24sin^3t i split it inot sin^2t and sint then used trig identity to get it to 1-cos^2(t) x sint and all i did worng from here was foregot to times by -1.

Your right it was just shy of 1 but the exact form i got it in was some nasty surd 16-(26/3)(root3)


Glad you tried it in the end. I had a go this morning and got that answer but wasn't confident as it was such messy working - and I was trying to do 3 things at once which is never a good idea when trying this sort of question :biggrin:
Original post by charlie.R.12
its fine i got the answer in the end i went wrong by just a silly error. when integrating -24sin^3t i split it inot sin^2t and sint then used trig identity to get it to 1-cos^2(t) x sint and all i did worng from here was foregot to times by -1.

Your right it was just shy of 1 but the exact form i got it in was some nasty surd 16-(26/3)(root3)


Must admit, Ive not worked it through parametrically (neither do I want to), but in x-y coords youre simply integrating
4 - x^2/9
from 3sqrt(3) to 6 (for the curved section) which aint hard. Similarly the intersection point is (3sqrt(3),1) and the grad of the tangent is -2sqrt(3)/3 whch gives the area of the triangle.
(edited 1 year ago)
Reply 7
Original post by mqb2766
Must admit, Ive not worked it through parametrically (neither do I want to), but in x-y coords youre simply integrating
4 - x^2/9
from 3sqrt(3) to 6 (for the curved section) which aint hard. Similarly the intersection point is (3sqrt(3),1) and the grad of the tangent is -2sqrt(3)/3 whch gives the area of the triangle.

It's not very pretty, which is why I wasn't volunteering an answer earlier until someone else had done it first :smile: The important thing with the parametrics is to remember that in going from left-to-right, t goes from pi/6 to 0, so if you get that wrong there's a negative contribution coming in. I did think of doing the cartesian equivalent to check my answer, but ran out of energy / time and other things took priority :biggrin:
Original post by davros
It's not very pretty, which is why I wasn't volunteering an answer earlier until someone else had done it first :smile: The important thing with the parametrics is to remember that in going from left-to-right, t goes from pi/6 to 0, so if you get that wrong there's a negative contribution coming in. I did think of doing the cartesian equivalent to check my answer, but ran out of energy / time and other things took priority :biggrin:


I hadnt done either originally, just a quick sketch, but the parametric description simply obfuscates things here.
Its a few lines to do it using the parabolic x-y representation.
(edited 1 year ago)
Reply 9
Original post by mqb2766
I hadnt done either originally, just a quick sketch, but the parametric description simply obfuscates things here.
Its a few lines to do it using the parabolic x-y representation.

tbh I only tried it that way because I had some expectation that either the OP or the markscheme expected it done that way, so I had a ready answer (if a bit rushed) if it came down to some nasty working to check :smile:

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