Question

. Find the A.P. whose 10th term is 5 and 18th term is 77.

Answer 1

Answer:

10th term = a+9d

5= a +9d

a= 5-9d

then, 18th term = a + 17d

18th term = 5-9d + 17d

77 =5 - 8d

77-5= 8d

72/8 =d

9. = d

then, a = 5- 9d

a= 5 - 9(9)

= 5 - 81

= - 76

ap = -76 , -67, -58 , -49......

Answer 2

☯ AnSwEr :

➝ A.T.Q

10th term of A.P (A10) = 5

➳ a + 9d = 5 ........(1)

Now,

18th term of the A.P (A18) = 77.

➳ a + 17d = 77 ......(2)

❁❁ Subtracting equation (1) and (2). ❁❁

We get,

➳ 8d = 72

➳ d = 72/8

➳ d = 9

❋❋ Put value of d in equation (1). ❋❋

➳ a + 9(9) = 5

➳ a + 81 = 5

➳ a = 5 - 81

➳ a = -76

$\therefore$ First term (a) = -76

Common Difference (d) = 9

➺ A.P = a, a + d, a + 2d .......

➺ A.P = -76, -67, -58 .......

⍟⍟⍟ A.P = -76, -67, -58 ...... ⍟⍟⍟