Question

4th and 5th term of the arithmetic sequence 25and 29 .a .what is commondifference ?b.what is the sum of 1st and 18th term of the sequence?​

Answer 1

Step-by-step explanation:

given a4 = 25 and a5 = 29

common difference d = a5 - a4

=> d = 29 - 25 => 4

a+3d = 25 => a + 3*4 = 25 => a = 13

[a4 = a + 3d]

S18 = n/2 { 2a + (n-1)*d }

=> S18 = 18/2 { 2*13 + (18-1)*4 }

=> S18 = 9 { 26 + 17*4 }

=> S18 = 9 { 26 + 68 }

=> S18 = 9*94

=> S18 = 188

therefore sum of first 18 terms = 188