a)9^n+9^n+1=10X3^2012
9^n(9^0+9^1)=10X3^2012
9^n(1+9)=10X3^2012
3^2n×10=10X3^2012
3^2n=3^2012
2n=2012
n=1006
b)6^n+6^n+3=217X6^55
6^n(6^0+6^3=217X6^55
6^n(1+216)=217X6^55
6^n ×217=217X6^55
6^n =6^55
n=55
c)7^n+1+7^n+2=8X7^117^n(7^1+7^2)=8X7^11
7^n(7+49)=8X7^11
7^n ×56=8X7^11
7^n ×7=7^11
7^n =7^10
n=10