Find the A.P. whose 3rd term is 18 and 12th term is 72.
Answer & explanation
Correct answer: option 1
In an AP ,
nth term
an = a1 + ( n - 1 )× d
18 = a1 + ( 3 - 1 )× d
18 = a1 + 2d ----(1)
72 = a1 + ( 12 - 1 )× d
72 = a1 + 11d ----(2)
On subtracting equation 1 from equation 2 .
9d = 72 - 18 = 54
d = 6
18 = a1 + 2 × 6
a1 = 6
So, Series is
6 , 12 , 18 , 24 , 30 , 36, 42, 48 , 54, 60 , 66, 72
Ans :- 6 , 12 , 18 ................