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Reply 1
koldtoast
hey
i've got a few maths problems that i cant seem to solve

Sequences and formulae:

find the value of n for which u has the given value in these:

1. u = 2n u = 256 answer: 8
2. u = 3n u = 2187 7
3. u = n(n-1) u = 380 20


And then, how to work out the formula for

1. 1/2, 1/3, 1/4
2. 2, 1.5, 1.333333, 1.25
3. 1, 2/3, 3/5, 4/7, 5/9


thanks a lot


Which types of series are these? Geometric or arithmetic?
Reply 2
koldtoast

And then, how to work out the formula for

1. 1/2, 1/3, 1/4
2. 2, 1.5, 1.333333, 1.25
3. 1, 2/3, 3/5, 4/7, 5/9


thanks a lot


i dunno bout the first lot, but i can try these

for fractions u hav to seperate the top and bottom

1)so 1/2, 1/3, 1/4 would be

1/n-1

2)2/1, 3/2, 4/3, 5/4 is the 2nd question in fraction form

so it would be n+1/n

3) 1, 2/3, 3/5, 4/7, 5/9

woulkd be n/the formula for odd numbas...which i cant seem to rememba...or wrk out at the moment!

let me know if ya need explainin on the above 2
Reply 3
Jonatan
Which types of series are these? Geometric or arithmetic?


the 2nd lot look like arithmetic!

the first...iu dunno
Reply 4
For the first, since its GCSE, you have to use trial and error.
256 = 2^n, try a few numbers and eventually get the right one.

For 3,
380 = n(n-1)
380 = n^2 - n
0 = n^2 - n - 380, which you can solve.
koldtoast
h
And then, how to work out the formula for

1. 1/2, 1/3, 1/4
2. 2, 1.5, 1.333333, 1.25
3. 1, 2/3, 3/5, 4/7, 5/9


thanks a lot


1.) nth term = 1/(n+1)
2.) nth term = (n+1)/(n)
3.) nth term = (n)/(2n-1)
Reply 6
JamesF
For the first, since its GCSE, you have to use trial and error.
256 = 2^n, try a few numbers and eventually get the right one.

For 3,
380 = n(n-1)
380 = n^2 - n
0 = n^2 - n - 380, which you can solve.


er, i dunno how to solve that lol
Reply 7
koldtoast
hey
i've got a few maths problems that i cant seem to solve

Sequences and formulae:

find the value of n for which u has the given value in these:

1. u = 2n u = 256 answer: 8
2. u = 3n u = 2187 answer: 7
3. u = n(n-1) u = 380 answer: 20


And then, how to work out the formula for

1. 1/2, 1/3, 1/4
2. 2, 1.5, 1.333333, 1.25
3. 1, 2/3, 3/5, 4/7, 5/9


thanks a lot


OK thanks i've figured out the second lot of questions involving fractions, but i just can't understand the first question (to do with sequences)

1. u = 2n u = 256 answer: 8
the way i see it....

256 = 2n
n = 128

i just dont see how the answer can end up being 8?
koldtoast
er, i dunno how to solve that lol


n^2 - n - 380 = 0

Using the quadratic formula:

a = 1, b = -1, c = -380

n = {1(+/-)sq.root [(-1)^2 - (4*1*-380)]}/2

n = [1 (+/-) sq.root (1 + 1520)]/2

n = [1 + sq. root (1521)]/2 = 20 OR
n = [1 - sq.roo t(1521)]/2 = -19

Solutions: n = 20 OR n = -19
koldtoast
OK thanks i've figured out the second lot of questions involving fractions, but i just can't understand the first question (to do with sequences)

1. u = 2n u = 256 answer: 8
the way i see it....

256 = 2n
n = 128

i just dont see how the answer can end up being 8?


It isn't supposed to be 2n, it is supposed to be 2^n

2^8 = 256

You must have copied it down wrong.
Reply 10
koldtoast
OK thanks i've figured out the second lot of questions involving fractions, but i just can't understand the first question (to do with sequences)

1. u = 2n u = 256 answer: 8
the way i see it....

256 = 2n
n = 128

i just dont see how the answer can end up being 8?

I thought you had just mis-read the question, if it said
u = 2^n ( 2 to the power n)
Then 8 would be the correct answer.

Btw to solve 3, if you cant solve quadratic equations, then like the others, you will need to use trial and improvement.
JamesF
I thought you had just mis-read the question, if it said
u = 2^n ( 2 to the power n)
Then 8 would be the correct answer.

Btw to solve 3, if you cant solve quadratic equations, then like the others, you will need to use trial and improvement.


You do quadratic equations at GCSE. We learnt that formula at GCSE, it came up in the exam as well.
Reply 12
koldtoast
OK thanks i've figured out the second lot of questions involving fractions, but i just can't understand the first question (to do with sequences)

1. u = 2n u = 256 answer: 8
the way i see it....

256 = 2n
n = 128

i just dont see how the answer can end up being 8?


i think the question is supposed to be 2^n rather than 2n.
Undry1
i think the question is supposed to be 2^n rather than 2n.


Yep.
bono
n^2 - n - 380 = 0

Using the quadratic formula:

a = 1, b = -1, c = -380

n = {1(+/-)sq.root [(-1)^2 - (4*1*-380)]}/2

n = [1 (+/-) sq.root (1 + 1520)]/2

n = [1 + sq. root (1521)]/2 = 20 OR
n = [1 - sq.roo t(1521)]/2 = -19

Solutions: n = 20 OR n = -19
Reply 15
hmm, i'm typing it straight out of the book, which btw is the Edexcel GCSE Maths Higher Course book for 2001 specs... page 292 exercise 14b

Q8. u = 2n u= 256
Q9. u = 3n u= 2187
Q10.u = n(n-1) u= 380
koldtoast
hmm, i'm typing it straight out of the book, which btw is the Edexcel GCSE Maths Higher Course book for 2001 specs... page 292 exercise 14b

Q8. u = 2n u= 256
Q9. u = 3n u= 2187
Q10.u = n(n-1) u= 380


Yes, but I bet it's a "2 with a small little n next to the top of it" not 2n.

Can't you see it's "2^" ?
Reply 17
2^n makes sense, and that is what the answer at the back would seem to support.

its weird but it REALLY looks like 2n instead of 2^n (with a little n towards the top right of the '2')... :confused: i'll see if i can scan the page somehow or something
koldtoast
2^n makes sense, and that is what the answer at the back would seem to support.

its weird but it REALLY looks like 2n instead of 2^n (with a little n towards the top right of the '2')... :confused: i'll see if i can scan the page somehow or something


Well obviously, as 2^n = 256.

If you can, scan in the page, i'd be interested to see it.
Reply 19
I just checked in my book and he/she is right the question is as they typed it...