Question

Need help with one quick question.

http://puu.sh/k6RWj/9cc0e86d9b.png

Answer 1

what you have here is an arithmetic sequence. That just means you have to add the same number to get to the next number.
If you will notice, the first figure has 3 line segments....the 2nd has 6....the 3rd has 9...so basically, you are adding 3 to every number to find the next number.
Now we are going to use this formula :
an = a1 + (n - 1)* d
a1 = first term = 3
d = common difference = 3
n = the number of the term you want to find = 20
now we sub
a20 = 3 + (20 - 1) * 3
a20 = 3 + 19*3
a20 = 3 + 57
a20 = 60

so your 20th term has 60 line segments