Use the sigma notation to write this summation in compact form:

2+4+6+8+10

@hartnn ? :)

Question

Use the sigma notation to write this summation in compact form:

2+4+6+8+10

@hartnn ? :)

hartnn · Answer

pattern ?

anonymous · Answer

|dw:1399228271388:dw|  ? :/

anonymous · Answer

+2, +2, +2 ?

hartnn · Answer

why 2 to 5 ?
lets make it easy and start with 1

do you know about arithmetic sequences ?

anonymous · Answer

the (n+2... equation? :/

anonymous · Answer

$$\sum_{k=2}^{5}2n$$

hartnn · Answer

$a_n = a_1 + (n-1)d$

hartnn · Answer

where a1 = 1st term
d= common difference

anonymous · Answer

ahh okay... yeah that looks familiar :)

anonymous · Answer

2n will always be even

2(1) = 2,
2(3) = 6
2(11) = 22

anonymous · Answer

ohhh okay,... did you use the arithmetic equation thingy to find that? :O

hartnn · Answer

this sequence is easy, you can find the n'th term mentally,
but for difficult one, you'll need to use general formulas

anonymous · Answer

Well, I know that an equation for an even series, where a(q) = a(q)*2

The equation for odds is a bit harder

hartnn · Answer

and limits are from n=1 to n =5
not from 2 to 5

anonymous · Answer

ahh okay... awesome!! thank you both !! :D

so we get this? |dw:1399228730077:dw|

hartnn · Answer

for the 3rd time : limits are from 1 to 5, not from 2 to 5

hartnn · Answer

you got how to get that "2k" ?

anonymous · Answer

ohh okay so |dw:1399228793050:dw|