Question 764514
The sum of n number of terms=Sn=n/2(2a+(n-1)d)
The n th term=a+(n-1)d

Given that
Sn=n/2(3n-17)

Take n=1
S1=1/2[3(1)-17]
=1/2(-14)
=-7
S1=a1
Therefore a1=-7
Now 
S2=2/2[3(2)-17]
=1(-11)
S2=-11
S2=a1+a2
-11=-7+a2
-11+7=a2
a2=-4

Also
a2=a+(n-1)d
Therefore,
-7+(2-1)d=-4
-7+d=-4
d=-4+7
d=3

Now
an=a+(n-1)d
substituting values of a, d in an 
an=-7+(n-1)3
=-7+3n-3
=3n-10//answer