FIND THE SUM
OF SEQUENCE
1,4,7.... 58
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Answer:
a=1
d=a2-a
=4-1
=3
an=58
Sn=n÷2(2a+(n-1)d
we have to find n value
an=a+(n-1)d
58=1+(n-1)3
58-1=(n-1)3
57÷3=n-1
19+1=n
n=20
Sn=n÷2(2a+(n-1)d)
Sn=20÷2(2(1)+(20-1)3
Sn=10(2+57)
Sn=10(59)
Sn=590
therefore Sn=590
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