the sum of the first 9 terms of an Ap is 81 and that of its first 20 terms is 400 . find the first term and the common difference of an Ap.( mene method to sahi lagaya par mera answer correct nahi hai please help me!)
Answers
Answered by
63
Answer:
Step-by-step explanation:
Solution :-
Let a be the 1st term and d be the common difference.
We know that,
S(n) = n/2[2a + (n - 1)d]
According to the Question,
1st part,
⇒ 2a + 8d =18 ....... (i)
2nd part,
⇒ 2a + 19d = 40 ...... (ii)
Subtracting eq (i) from (ii), we get
⇒ (2a + 19d) - (2a + 8d) = 40 - 18
⇒ 11d = 22
⇒ d = 2
Putting d's value in Eq (i), we get
⇒ 2a + 16 = 18
⇒ 2a = 18 - 16
⇒ 2a = 2
⇒ a = 2/2
⇒ a = 1
Hence, 1st term is 1 and common difference is 2.
Answered by
62
GIVEN :-
TO FIND :-
The first term and the common difference of the A.P.
SOLUTION :-
Subtracting eq.(i) from eq.(ii) :-
Putting the value of d in eq.(i) :-
Saby123:
Awesome ❤
Similar questions