how many tems of AP 21,18,15 ...must be added to get the sum 0
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a=21
d=18-21=-3
Sn=0
Sn=n/2(2a+(n-1)d)
or,0=n/2(2×21+(n-1)-3)
or,0=n(42-3n+3)
or,0=n(45-3n)
or,0=45n-3n2
or,3n2=45n
or,3n=45
therefore,n=45÷3=15 ans THANKS ✌✌
d=18-21=-3
Sn=0
Sn=n/2(2a+(n-1)d)
or,0=n/2(2×21+(n-1)-3)
or,0=n(42-3n+3)
or,0=n(45-3n)
or,0=45n-3n2
or,3n2=45n
or,3n=45
therefore,n=45÷3=15 ans THANKS ✌✌
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