Answers

2016-02-07T00:16:58+05:30
Given:Sn=5n^2-3n
to find :the A.P and its 12th term

S1=5(1)^2-3(1)=2
S1=Sum of first term=first no. of the A.P.
so a1=2

S2=5(2)^2-3(2)
=14

S2=a1+a2
so a2=S2-a1
=14-2
=12

d=a2-a1
so d=12-2
=10

so a3=a2+10=12+10=22
and a4=a3+10=22+10=32

so A.P. is 2,12,22,32....

an=a+(n-1)d
so a12=2+(12-1)10
=2+(11*10)
=2+110
=112

so A.P. is 2,12,22,32...
and a12=112
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