Question

1. Find the sum of the first 21 terms of the arithmetic sequence given by the formula an = n+5
I see that I have to plug in numbers and get the terms...but i'm sure there's a shorter way to do this instead of plugging in 21 numbers.

2. The following infinite geometric series will have a finite sum: 1001/6 + 1001/36 + 1001/216 + 1001/1296
Not sure...

Answer 1

http://www.regentsprep.org/Regents/math/algtrig/ATP2/ArithSeq.htm

Answer 2

you should know the nth sum of an A.S. is

Sn = n/2 (2a + (n-1)d)
Your sequence has
a=6
d=1

For the G.S. you must have |r| < 1.
What are a,r for this sequence?

Answer 3

Is the answer 336?

Answer 4

That's what I get.

Answer 5

Yes,thanks

Answer 6

Pls can u help me to solve: x+y+z=1,x^2+y^2+z^2=34 and x^3+y^3+z^3=94