Question

2x4+4x6+6x8.........to n terms..... how to get the 20th term of this sequence

Answer 1

Un=4n^2+4n
U20=4(20)^2+4(20)
=1680

Answer 2

Un=4n(n+1)

Answer 3

how to reach that equation??

Answer 4

8 24 48 ...
16 24
8


maybe, then we take the first diagonal and apply some pascal to it with any luck

Answer 5

When we do sequences(or series) we always need to take the term number into our thinking process. So, naturally, we look at the first term and say 2 times one is 2 so 2n is part of the equation somehow.

Answer 6

sry, i have a way of doing it, but its not that easy to explain...once you do lots of series and sequences, there tends to be a patter like usually n+1 or n+2 or 2n is involved. Just checks work with my method.

Answer 7

8*nC0+16*nC1+8*nC2

this is similar to what i recall; prolly needs to be refreshed to be accurate tho

Answer 8

8*1+16n+8n(n-1)/2 lets see if this is a good recollection lol

8 + 16n +4n^2-4n

4n^2 -12n +8 ?

Answer 9

when n=0, we get 8

when n=1 we get 0 ... doh!!

Answer 10

2,4,6 = 2+2(n-1)
x
4,6,8 = 4+2(n-1)

an = (2+2n-2) * (4+2n-2)

a20 = (2+2(20)-2)*(4+2(20)-2)
= (2(20))*(2+2(20))
= (40)*(42)
= 1680

?? yay, we match now

Answer 11

right,,,thanx mates