Question

the sum of the first 9 terms of an ap is 81 and the sum of its first 20 terms is 400 find the first term and the common difference of the AP​

Answer 1

Step-by-step explanation:

I Hope this will help you

Answer 2

$\Large{\textbf{\underline{\underline{According\;to\;the\;Question}}}}$

Assumption

First term be p

Common difference be d

Now,

As we know that,

First Situation,

2p + 8d =18 ....... (1)

Second Situation,

2p + 19d = 40 ...... (2)

Now,

Subtract (1) from (2),

(2p + 19d) - (2p + 8d) = 40 - 18

11d = 22

d = 2

Substitute the value of d in (1),

2p + 16 = 18

2p = 18 - 16

2p = 2

p = 2/2

p = 1

Therefore,

First term = 1 and common difference = 2