Question

the nth term of an ap is represented by an= 3n + 1 find the ap and the sum of first 20 terms

Answer 1

Answer:

The A.P is 4,7,10,13.......

The sum of first 20 terms is 650

Step-by-step explanation:

n=1 => a1 = a = 3(1)+1 =4

n=2 => a2 = a+d = 3(2)+1 =7

n=3 => a3 = a+2d = 3(3)+1 =10

n=4 => a4 = a+3d = 3(4)+1 = 13

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=> a= 4, d=7-4=3,n=20

S20 =

$= \frac {20}{2} (2 \times 4 + ((20 - 1) \times 3)) \\ \\ = 10(8 +(19 \times 3 )) \\ \\ = 10 \times 65 \\ \\ = 650$

Hope this helps!!

All the best!!!!