# The sum of first m terms ...

The sum of first m terms of an AP is (4m2-m).If its nth term is 107,find the value of n .Also, find the 21st term of this AP.

S1=a=3 by putting m=1 in 4m²-m S2=14 by putting m=2 in 4m²-m A2 = S2-S1 A2= 11 AP is 3,11,19...... d= 8 an= a+(n-1)d Now solve for n 107=3+(n-1)8 n=14 21st term = 3+20×8 =163 Hope you will satisfied with my answer☺️☺️

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