.
11. Find the sum of the arithmetic sequence 2, 4, 6, 8, ..., 70.
On arithmetic progressions, read the lesson Arithmetic progressions in this site.
The given progression is AP with the first term 2 and the common difference 2.
It contains all even integers between 2 and 70, inclusively.
The number of the terms is = 35.
Use the formula for the sum of an AP
S = = .
Calculate it yourself.
12. Find the sum of the geometric sequence 42, 7, 7/6,. . . , 42*(1/6)^8
The last term of the progression was written INCORRECTLY. I fixed it.
On geometric progressions, read the lesson Geometric progressions in this site.
The given progression is GP with the first term 42 and the common ratio .
The number of the terms is 9.
Use the formula for the sum of a GP
S = = = = = = .
Calculate it yourself.