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Original poster

Help with 2 sums!!!

12 replies

bkgirl · 01/09/2014 18:58

Hello, I am dreadful at maths and my son has come home, he could do most of his homework but got stuck on the last one. I am clueless. If anyone could help - it would be appreciated.

The nth term of a sequence is represented by N²-6
a) Find the 12th term of the sequence.
b) Which term of the sequence will equal 219?

OP posts:
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PastSellByDate · 04/09/2014 13:37

Hi bkgirl:

If you haven't come across it - than I highly recommend BBC Bitesize (GCSE revision tips):

nth term advice here: www.bbc.co.uk/bitesize/ks3/maths/algebra/linear_sequences/revision/3/

Khan Academy (entirely free) has useful videos explaining how to do various calculations - for nth term there are several - but start here: www.khanacademy.org/math/precalculus/seq_induction/deductive-and-inductive-reasoning/v/u12-l1-t3-we1-inductive-reasoning-1 - this is an American-based tutorial - but math is maths, if you see what I mean.

this site generates practice questions as well: studymaths.co.uk/keytopics/nthterm.html

I think the problem here is that your DS either missed the explanation bit or none was given - next time try typing in on BBC Bitesize or Khan Academy the thing you're struggling with and see if there is some help there.

HTH

noblegiraffe · 01/09/2014 19:47

Nth terms of linear sequences is basic stuff. You're right, quadratics are on the GCSE syllabus but I've never seen them come up - I recently did them with my further mathematicians so got confused, but they do much harder questions.

titchy · 01/09/2014 19:37

Why do you say that noble - that looks quite a straightforward question? Dcs both did nth term in year 8 iirc.

Original poster
bkgirl · 01/09/2014 19:36

He is doing GCSE maths but not further maths.
I think he is doing quadratic sequences as part of this syllabus.

OP posts:
noblegiraffe · 01/09/2014 19:14

Were the rest of the questions about quadratic sequences or just linear ones? Is he top set GCSE doing further maths?

If not, I suspect the question was included in error.

Original poster
bkgirl · 01/09/2014 19:12

Thank you so much.
He is 14, surely the teacher would have showed him how to do this. He said he was paying attention but wasn't explained this bit. I have had about 3 hours sleep in the last 24 so having trouble even being coherent. It looks like I am going to have to revise with him this year. Oh dear me.

OP posts:
noblegiraffe · 01/09/2014 19:10

Scratch that, I forgot it was a sequence question, n can only be positive!

noblegiraffe · 01/09/2014 19:10

There are two answers to the second, don't forget the negative square root.

noblegiraffe · 01/09/2014 19:09

You should work out the answer for the first one, I mean! Or rather, your DS should.

ilovepowerhoop · 01/09/2014 19:09

a) do you think that mean 12²-6 = 144-6 = 138
b) so it means N²-6 = 219 so N² = 219+6 so N² = 225 so N= square root of 225 = 15

Potcallingkettle · 01/09/2014 19:08

In A, n=12, so do
(12 x 12) - 6
=144-6
=138
In B, work the other way
n2 - 6 = 219
n2 = 225
n = 15
Sorry the 2 is big, am on my mobile.

noblegiraffe · 01/09/2014 19:07

How old is your DS?
for the first, put in 12 as N, so 12 squared - 6

For the second, n squared - 6 = 216. Solve the equation.

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