Question

If a1 a2.....an form an AP in which an=4+5n Find the sum of first 20 terms​

Answer 1

Answer:

1130

Step-by-step explanation:

Given, an = 4 + 5n

Hence, a1 = 4 + 5x1 = 9

and, a2 = 4 + 5x2 = 14

Thus, first term = a = 9

and, common difference = d = a2 - a1 = 14 - 9 = 5

Sum of first 20 terms =

= (n/2){2a + (n-1)d}

= (20/2){2x9 + (20-1)x5}

= 10{18 + 95}

= 1130

Answer 2

Answer:

Sum of first 20 terms = 1,130

See the attached image for detailed steps

Step-by-step explanation:

Hope it will help you !!!