Question

if the3rd term of AP is 18band 17th term is42 then the first term is​

Answer 1

a+2d=18

a+16d= 42

Subtracting 1st eq by 2nd, we get

d=12/7

then a = 18- 24/7

Answer 2

Question:-

if the3rd term of AP is 18band 17th term is42 then the first term is

${\red{\underline{\underline{\bold{Answer:-}}}}}$

Let a be the first term and d be the common difference

Then

According to the question !!!!

a + 2d = 18 (1)

a + 6d = 30 (2)

from 1 and 2

4d = 12

d = 3

Substitute it in 1

a + 6 = 18

a = 12

so 17 term

a + 16d = 12 + 16×3 = 12 + 48 = 60

hence your answer is 60..