How many terms of A.P 2,7,12....must be taken to give a sum of 245
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a= 2 , d= 5 Sn= 245
Sn= n/2{2a+(n-1)d}
245= n/2(4+5n-5)
245= n/2(5n-1)
490= 5n²-n
5n²-n-490=0
by quadratic formula
a= 5 , b= -1 , c= -490
x = 1+ √1-9800 / 10
x=
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