Help with 2 sums!!!

[bkgirl]

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?

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.

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.

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

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

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

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

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.

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.

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

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

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.

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