# Talk

## HELP with using the nth-term rule

(9 Posts)
kid Mon 26-Sep-11 19:52:39

DD has to complete this HW but doesn't understand it and I haven't ever used it before so don't know either!

The 2 questions are:

1) n+2 1st term, 2nd term, 3rd term, 4th term, 5th term

2) 5xn 1st term, 2nd term, 3rd term, 4th term, 5th term

I have attempted to get the answers but figure I'm wrong (I might not be but I have no faith in my answers atm)

So, can some clever MNer come and give me a couple of answers so I know if I've got it or not.
I've read some links online and they are just confusing me even more

musttidyupmusttidyup Mon 26-Sep-11 19:56:50

N represents the 'pattern number' so if the rule for the nth term is n+2
First term is 1+2=3
second term 2+2=4
3rd term =5 etc
So it's 3 4 5 6 7.....

For nth term 5n it means 5xn so
1st term 5x1=5
2nd term 5x2=10 etc
So 5 10 15 20 25.....

HTH

kid Mon 26-Sep-11 20:01:05

Thanks musttidyup, I did get those answers for the 5xn, not sure about the n+2 though.

How about n-7, that will go into negative numbers won't it?
While you are there helping , how about
(3xn)-2
8+(2xn)
n/2 (divide)
0.3xn
n squared

I seriously hope she never gets hw like this again, its horrible!
I really appreciate your help, DD will think I am so clever

musttidyupmusttidyup Mon 26-Sep-11 20:46:38

Ok to go into negatives so, yes, n-7 gives -6, -5, -4, -3, -2

(3xn)-2
x by 3 first then -2, so
1st term is (3x1)-2 = 1
2nd term is (3x2)-2 = 4
3rd term (3x3)-2 = 7
so it's 1, 4, 7, 10, 13

8+(2xn)
1st term is 8+(2x1)=10
2nd term is 8+(2x2)=12
3rd term 8+(2x3)=14
so it's 10, 12, 14, 16, 18

n/2 (divide)
1st term is 1/2 = 0.5
2nd term is 2/2 = 1
3rd term 3/2 = 1.5
so it's 0.5, 1, 1.5, 2, 2.5

0.3xn
1st term is 0.3x1=0.3
2nd term is 0.3x2=0.6
3rd term 0.3x3=0.9
so it's 0.3, 0.6, 0.9, 1.2, 1.5

n squared - times it by itself, ie nxn
1st term is 1x1=1
2nd term is 2x2=4
3rd term 3x3=9
so it's 1, 4, 9, 16, 25

Fun eh?

kid Mon 26-Sep-11 21:06:06

thank-you
As I was writing the answers out, I was seeing if I came up with the same answer as you before looking at your answers and I did so I think I am okay to do these now. I don't see the point of them but I guess if the teacher wants DD to do them, then DD will do them.

I'll explain a couple to her tomorrow and see if she can work out the rest by herself.

kid Mon 26-Sep-11 21:16:56

I was just looking at what DD had put for her answers.
She'd wrote for n+2 1st term 2x1+2 so she was nearly right on that one.

For 5xn she'd put 1st term 5x1, 2nd term 2x5, 3rd term 5x3 so she was more or less right on that one.

She got scared off when she saw n-7 but she'll be fine now I can explain confidently to her how its done I don't think she bothered looking past the -7 one to the rest of the numbers!

musttidyupmusttidyup Mon 26-Sep-11 21:19:42

No problem

chatee Tue 27-Sep-11 11:02:57

hiya kid,
sorry had to giggle at your post as I was in exactly the same predicament two weeks ago! my dh just said to my dd "you know homework is your mother's department!" and then confessed to me he didn't have a clue- a bit shocked as it was the first piece of maths homework from secondary so he now won't even look at any questions it's a "wait til your mother gets home" scenario.

Talking to dd and getting her to play the role of the teacher(teaching me) she did actually know what she was doing but it's a confidence problem more than a maths problem(I think and hope)as I really am not mathematically minded(starting to worry as it is a computer and maths specialist school eek)

dd did the same last night(this time angles!)- but when I sat down with her and did the role play again she completed the work quite easily

Lets hope we(and good old mumsnet) can help each other through this !

kid Tue 27-Sep-11 20:36:47

Dd just completed the hw and we are now very good at using that method.
Dd thinks I got the answers from google, she has no faith in me

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