d=(18-6)/3=4~~~~an=2+4*(n-1)=4n-2b1+1/2b1=1~~~~~~b1=2/3T(n+1)-Tn=b(n+1)=1/2(bn-b(n+1))~~~~b(n+1)=1/3bn~~~~~bn=2*(1/3)^ncn=(4n-2)*2(1/3)^n=(2n-1)(1/3)^nc(n+1)=(2n+1)(1/3)^(n+1)c(n+1)-cn=(1/3)^n((2n+1)/...