# Jump in series

1. Oct 4, 2014

### hello_math

Hello All

I have got a very basic Math query here and hope people will not get turned off with the nature of this simple query.
My query goes like this:
variable X makes jump by factor +4.
at the same time, Y makes a jump by factor +2

in coordinate terms, I would have a series like :
(4,2) (8,4) (12, 6) (16,8) (20,10)....and so on
I would like to know the generic formula for calculting this coordinate series...for example,if Y is (say) 2867544 , then what should be X ? ( also vice versa )

can anyone tell me a formula for this please
...and hope the question was clear .

Thanks
Rick

2. Oct 4, 2014

### Staff: Mentor

The jumps are not by a "factor" of 4 or 2. Factor implies things being multiplied. Here you're just adding 4 or 2 to the previous x or y value, respectively.
All of these points are on a straight line whose equation is y = (1/2)x.

3. Oct 4, 2014

### LCKurtz

And, since $x_n=4n,~n=1,2,3...$ your coordinate pairs are $(4n,2n)$.

4. Oct 5, 2014

### hello_math

Thanks all . Yes my 'factor' impliction was wrongly used indeed :(
there was another mistake of mine with the series. the actual points on the straight line are : ( 0,2,) ,(4,4) ,(8,6)....and so on.
and I cant use y = (1/2)x here.
and I dont think I can use (4n,2n) either. [ e.g for the 20th 'jump' , it {as per the 4n,2n) formula } should be 80,40..but actually the coordinates are (76,40) ]
so what can I use here ....and what if 'n' is not given at all. How do I go about . In other words if only Y coordinate has been given for e.g Y is (say) 2867544 .

I am asking this on behalf of my 12 year old kid, who has only a 'jump' till Y coordinate =62 in his textbook. Now this can be easily done with the fingers and the homework is finished :)....but I was looking for a more generic formula here & completely out of curiosity.

Thanks

5. Oct 5, 2014

### LCKurtz

Try $(4(n-1),2n)$.

6. Oct 6, 2014

### hello_math

allright and anyway to find the 'n' too ?

7. Oct 6, 2014

### LCKurtz

I don't understand what you are asking. $n$ can be $1,2,3,4...$. Find what $n$?

8. Oct 7, 2014

### hello_math

nope nothing
I was a bit confused myself here.
anyway...Super. Lets close this issue here now

and Thanks all.!