Question 12
Find the last digit of $1+3^1+3^2+3^3+\cdots+3^{2020}+3^{2021}$.
HKIMO 2026 THPT (Grades 10–12 shared) National Preliminary Set 02 Question 12
HKIMO · HKIMO 2026 THPT (Grades 10–12 shared) National Preliminary Set 02
HKIMO · HKIMO 2026 THPT (Grades 10–12 shared) National Preliminary Set 02