Question

hmm

Answer 1

that's a big one...

Answer 2

its kinda simple..i m just doing the same stupid mistake on all of the problems and i can't figure out what i m doing wrong...

Answer 3

why are you using the quadratic formula?

Answer 4

To find x which gives me n..?

Answer 5

lol you multiplied the right hand side by 2...you should multiply the left hand side by 2 because you cross multiply

Answer 6

wouldn't you solve "an = 4n + 1 (the rule of the series) " out for n?

Answer 7

Oh..thats probably what i m doing wrong on everything..lemme see.

nd doom, um u need an..tho?

Answer 8

ahh

Answer 9

I got 28.06..which is still wrong.. :(

Answer 10

you should ask amistre64

Answer 11

he can help

Answer 12

ok..@amistre64

Answer 13

what does "an" supposed to mean?

Answer 14

an is the rule..

Answer 15

is it constant?

Answer 16

um yeah?

Answer 17

Sn = n (a1 + an) /2
3320 = n (5 + 4n + 1)/2
3320 = 5n + 4n^2 + 1n/2
3320 = (5n + 4n^2 + 1n) *2 3320=(5n+4n^2+1n)/2
3320 = 10n + 8n^2 + 2n 3320= (4n^2 +6n)/2 Combine like terms
3320 = 8n^2 + 12n 3320 *2= 4n^2+6n
0 = 8n^2 + 12n – 3320 6640= 4n^2+ 6n
0 = 4(2n^2 + 6n - 830) 4n^2+6n-6640 Solve from here
disregard a negative answer :>

Answer 18

Um It would be 0 = 4(2^2 + 3n - 830) Right?

Answer 19

You're factoring it wrong.

Answer 20

3320 = n/2(2 x 5 +(n -1) x 4)

3320 = n/2(4n + 6)

3320 = 2n^2 + 3n

or

2n^2 +3n - 3320 = 0

using the general quadratic formula

n = (-3 +- 163)/4 n = 40 or - 41.5

use n = 40

Answer 21

But when you factor 12 from 4, you get..3

Answer 22

I'm not a fan of quadratic formula myself but you can still use that method to solve this equation. I use factoring a lot and here's how I solve your problem.
4n^2+6n-6640 can be reduced to
2n^2+3n-3320 by dividing everything to 2
I got:
(2n +83) (n-40)
Normally there are 2 answers for this:
n= -41.5 and n= 40
a negative answer doesn't make sense so cross it out which leave you only 40.

Answer 23

Thanks guys! I did a mistake in my calculation thanks! :D

Answer 24

Your welcome!
Try to minimize your mistake next time. That's how math works, a mistake can lead to a wrong and confusing answer. Best of luck!

Answer 25

Ill try! :) Thanks!1