Question

the sum of the first n terms of an ap 5n^2-3n find the ap and hence find its 12th term

Answer 1

Answer:

Required AP is

2, 12, 22...

and 12th term is = 112

Step-by-step explanation:

Given is

$5n^2-3n$

To get the AP, Let n = 1 and 2

$5(1)^2 - 3(1)=2  and \\5(2)^2-3(2) =14$

here we got

a = 2

and, sum of first two term is 14

$a_{1} + a_{2} = 14\\  2 +a_{2} = 14\\a_{2} = 12$

also

d = a_{2} - a_{1} = 12 - 2 = 10

Hence the required AP would be

2, 12, 22...

NOW, 12th term will be

a_{n} = a +(n-1)d

a_{12} = 2 + (12 -1)10 = 112

hope it helps

jerri