Let the first term be a and common difference is d,
Now sum of 13 term is
13/2(2a + 12d)= 13/2*2*40=520
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• Let the first term of an A.P. be a and common difference is d. So the 7th term of the A.P. is 40=> a+6d =40.
Sum of first 13 terms = 13/2(a +(a+12d))= 13/2(2a+12d) =
13/2(2)(a+6d) =13(a+6d) =13(40)=
• 7th term = 40To Find :
• Sum of the first 13th term = ?Solution :
Let us assume that the first term be a and the common difference be d.
We know that,
Therefore, sum of the first 13th term is 520.⠀⠀━━━━━━━━━━━━★ Additional Information :
• The general form of an AP isa, a + d, a + 2d, a + 3d ....
• Formula to find the nth term of an AP isTn = a + (n – 1) d
where,tn = nth terma= the first term d= common differencen = number of terms
• Formula to find the numbers of term of an AP isn= [ (l-a) / d ] + 1
where,n = number of termsa= the first terml = last termd= common difference⠀⠀━━━━━━━━━━━━
Firstly, we know that formula an A.P;
Where as;a is the first term.d is the common difference.n is the term of an A.P.
Now, using formula of the sum of an A.P;
The sum of first 13th term is 520 .