Question

Arithmetic and geometric series -Find the sum of the first 50 terms of the following series, to the nearest integer.

13,21,29,...

Answer 1

10,450

Explanation:

21-13=8 and 29-21=8

So this is aritmetic series where a₁ = 13, and r = 8

Sum of the first n terms:

`S_n=(a_1+a_n)/(2)\cdot n=(a_1+a_1+(n-1)r)/(2)\cdot n=(2a_1+(n-1)r)/(2)\cdot n\\\\\\S_(50)=(2\cdot13+(50-1)\cdot8)/(2)\cdot50=(13+49\cdot4)\cdot 50=10,450`