Find the sum of first 20 multiples of 7
Answers
Answered by
65
the first 20multiples of 7 are in AP with their common difference equal to 7
ist term = 7
common difference = 7
sum
= 20/2[2(7)+(20-1)(7)]
=10(14+133)
=10 x 147
=1470
ist term = 7
common difference = 7
sum
= 20/2[2(7)+(20-1)(7)]
=10(14+133)
=10 x 147
=1470
Answered by
56
7 ,14,21,..140 are first 20 terms
these are in AP
first term =a = 7
n= 20
d= a2-a1 = 14-7=7
last term = l=140
sum of n terms Sn = n/2 [a+last term]
s20 = 20/2[7+140]
=10*147
=1470
these are in AP
first term =a = 7
n= 20
d= a2-a1 = 14-7=7
last term = l=140
sum of n terms Sn = n/2 [a+last term]
s20 = 20/2[7+140]
=10*147
=1470
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