seventh term of an ap is 40 the sum of its first 13 terms is
Answers
Answered by
44
Answer:520
Explanation:
7th term of AP= 40
[a+6d]=40 -------------<i>
sum of 13 terms=
n/2{2a+[n-1]d}
=13/2{2a+12d}
=13[a+6d]
=13*40 <from i>
=520
Answered by
10
Answer:
520 is the answer .
Explanation: Hey mate,here you go....
a7 = 40
an = a+(n-1)d
40 = a+(7-1)d
40 = a + 6d ---(1)
To find the sum of first 30 terms:-
Sn= n/2{2a+(n-1)d}
Sn13 = 13/2{2a+(13-1)d}
= 13/2(2a+12d) [taking 2 common in next step]
= 13/2 ×2(a+6d)
Now from ----(1)
= 13/2 × 2 (40)
= 13×40
Sn 13 = 520 is the answer
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