You are Here: Home >< Maths

# sequence watch

1. hi can someone help me on this question ;-

n sum r=1 (4r-3) >2000?? i got 23 but my book is getting 36 please help thanks
3. somebody?
4. What have you done so far?
5. (Original post by ghostwalker)
I get n=32
how cause i got a quadratic formula
6. (Original post by msmith2512)
What have you done so far?
can u show me bro
7. I agree with ghostwalker and 32.

If you want some help then show me what you have done so far and I might be able to help you understand. Just giving you the answer won't help you in future.
8. (Original post by msmith2512)
I agree with ghostwalker and 32.

If you want some help then show me what you have done so far and I might be able to help you understand. Just giving you the answer won't help you in future.
ok i got for the first 3 terms 1,5,9
then i used the sum formula
sn=n/2(2+4n-4)=2000
sn=n(8n-4)=4000
8n squared -4n-4000
quadratic formula so i got 23
9. (Original post by otrivine)
ok i got for the first 3 terms 1,5,9
then i used the sum formula
sn=n/2(2+4n-4)=2000
OK up to here.

sn=n(8n-4)=4000
At this point you've multiplied by 4 on the LHS (you got rid of the 2 and multiplied the bracket by 2), and by 2 on the RHS.
10. (Original post by ghostwalker)
OK up to here.

At this point you've multiplied by 4 on the LHS (you got rid of the 2 and multiplied the bracket by 2), and by 2 on the RHS.
Yes is that correct?
11. (Original post by otrivine)
Yes is that correct?
No.

What ever you do to one side of an equation, you must do to the other to maintain equality.

So, multiplying one side by 4, and the other by 2 isn't a valid option.

I'd suggest just simplifying the LHS and dividing what you have in the brackets by the 2.
12. (Original post by ghostwalker)
No.

What ever you do to one side of an equation, you must do to the other to maintain equality.

So, multiplying one side by 4, and the other by 2 isn't a valid option.

I'd suggest just simplifying the LHS and dividing what you have in the brackets by the 2.
So u mean multiply both sides by 2 but I did right?
13. (Original post by otrivine)
So u mean multiply both sides by 2 but I did right?
No, you multiplied one side by 4.
Looking at one of two of your other threads, it looks like you're struggling with basic algebraic maniplulation; and that's an issue you really need to address.

I'll post the working for this one using two different methods.

Starting from

Let's simplify that to --------------(X)

A)

If we multiply through by 2 on each side, we get:

Then expanding brackets:

And we can divide through by 2 and rearrange to get

B) Alternatively, from (X), we could have

divided the 2 into the brackets to get

Expanding the brackets now, and rearranging we have, as before.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: September 26, 2011
Today on TSR

### Makeup, beauty and skincare

Best of Black Friday 2018

### University open days

Wed, 21 Nov '18
• Buckinghamshire New University
Wed, 21 Nov '18
• Heriot-Watt University
Wed, 21 Nov '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams