Question

The sum of the first and 17th term of an arithmetic sequence is 40.The sum of first and 18th term is 43
A) what is the common difference
B) what is the sum of 7th and 11th term ​

Answer 1

answer a) is 3

answer b)is 44

Step-by-step explanation:

AP equation goes like

Tn= a + (n-1)d

where a is first term and Tn is nth term, d= common difference so,

T17(means 17th term)= a + 16*d

but T17 + a= 40 ... equ 1

also T18 + a = 43 ... equ 2

on substracting equation 1 from 2, you get..

T18 - T17 + a -a =43 - 40 =3 ... equ 3

so common difference = 3

for finding a

T17 = a + 48

so it means ..

a+48 +a =40

so 2a = - 8

so a= -4

question 2:

T7= a + 6d = -2 + 6*3 = 16

T11 = a + 10 d = -2 + 10*3 = 28

T7+T11 = 44