Question

the sum of the 1st and 17th terms of an arithmetic sequence is 40.the sum of its 1st and 18th term is 43( question no 1.) what is its common difference? (question no.2) what is the sum of its 7th and 11th terms?(fquestion no.3)find it's 9th term?​

Answer 1

Answer:

answer 1 is 3

answer 2 is 44

answe 3 is 22

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

question 3:

T9 = a + 8*d = -2 + 8*3= -2 + 24 = 22

Answer 2

Answer:

Correction Question 3.

9th term = a+8d

=-4+8*3

=-4+24

= 20.