Q. 2

Find the

Answer :

Given: 10 th term of A.P = T 10 = 5
18 th term of A.P = T 18 = 77

Now we know that,

T n = a + (n – 1)d

Therefore,

5 = a + (10 – 1) d
a + 9d = 5 … (1)
And,

77 = a + (18 – 1) d
a + 17d = 77 ….(2)

Now,

Subtract (1) from (2),

(a + 17d) – (a + 9d) = 77 – 5
a + 17d – a – 9d = 77 – 5

8d = 72

d = 9

Now,

a + 9d = 5
a + 9 × 9 = 5
a + 81 = 5

a = 5 – 81

a = – 76

T 1 = –76 + (1 – 1)9 = –76

T 2 = –76 + (2 – 1)9 = –67

T 3 = –76 + (3 – 1)9 = –58

The A.P. is – 76, - 67, –58,………….

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