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# PLZ help me with maths coursework watch

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1. hi,ppl. i m studying in year 10, doing my gcses. in maths we r doing coursework on stacking boxes. it is about sequences and nth term.i m stuck on the bit where i have to explain and make a link between the formula i have obtained and drawing which are in 3 dimension.
I am attaching drawings of my stacks in 3D where n=3 n=4
Plz help me. I dont know how to expain in terms of n, where n^2 and n antd etc are in the stack. the cubis formula for 3D is
un=4n^2 - 7n + 4
Attached Images
2. maths coursework black and white.pdf (53.5 KB, 98 views)
3. Ill gladly help u, but this goddam computer im sitting on don't have acrobat reader! upload a .doc or other file instead and ill have a peak. (did almpost the same kind of problem not too long ago)
4. by obversation we can see the term does not 'go up' by a constant, therefore we are dealing with a quadratic (an ax^2)
we can see that when n=1, Un=1
n=2, Un=6
n=3, Un= 19

when n=1, a*n^1 + b*n + c = 1 => a+b+c=1
when n=2, a*n^2 + b*2n + c = 6 => 4a + 2b + c = 6
when n=3, a*n^3 + b*3n + c = 19 => 9a + 3b + c = 19

three equations, 3 unknowns, I'll let someone else (or you!) work it out. It should work out as Ive done it here but i cba to type it up now.

Rev
5. (Original post by Revelation)
by obversation we can see the term does not 'go up' by a constant, therefore we are dealing with a quadratic (an ax^2)
we can see that when n=1, Un=1
n=2, Un=6
n=3, Un= 19

when n=1, a*n^1 + b*n + c = 1 => a+b+c=1
when n=2, a*n^2 + b*2n + c = 6 => 4a + 2b + c = 6
when n=3, a*n^3 + b*3n + c = 19 => 9a + 3b + c = 19

three equations, 3 unknowns, I'll let someone else (or you!) work it out. It should work out as Ive done it here but i cba to type it up now.

Rev
lol, i ve done it. it is in the attachment look in it. btw here u need to use cubic formula un = an^3 + bn^2 + cn + d
i Ve found the formula. But now i need to explain it in terms of n^3, n^2 and n.

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