Question

Find the AP was 10th is 5 and 18th term is 77

Answer 1

Given that;

a(10) = 5

a(18) = 77

As we know;

a(10) = a + (n-1) d = a + 9d

A(18) = a + (n-1)d = a + 17d

We can write it as:-

a + 9d = 5                                       ..(1)  

and a + 17d = 77                            ..(2)

Subtract both equations to get

a - a + 17d - 9d = 77-5

8d = 72

d = 9

Hence

a = 5 - 9d = 5-81 = -76

Hence, the AP is -76, -67, -58, - 49, -40, -31, -22, -13, -4, 5 etc.