an=a1q^(n-1)
=1*(1/3)^(n-1)
=(1/3)^(n-1)
a(n-1)=(1/3)^(n-2)
an-a(n-1)
=(1/3)^(n-1)-(1/3)^(n-2)
=1/3*(1/3)^(n-2)-(1/3)^(n-2)
=(1/3)^(n-2)*(1/3-1)
=2/3*(1/3)^(n-2)
=2(1/3)^(n-1)
an=a1q^(n-1)
=1*(1/3)^(n-1)
=(1/3)^(n-1)
a(n-1)=(1/3)^(n-2)
an-a(n-1)
=(1/3)^(n-1)-(1/3)^(n-2)
=1/3*(1/3)^(n-2)-(1/3)^(n-2)
=(1/3)^(n-2)*(1/3-1)
=2/3*(1/3)^(n-2)
=2(1/3)^(n-1)