Question

find the sum of 15 terms of an arithmetic progression 2, 7, 12.....using formula​

Answer 1

Answer:

a=2 , d=a2 - a1=7-2=5

S=n/2 [2a+(n-1)d]

S=15/2 [2×2+(15-1)5]

S=15/2 [4+14×5]

S=15/2[4+70]

S=15/2×74

S=555

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