- #1
Quadrat
- 62
- 1
Homework Statement
Find the last two digits in ##12345^{6789}##
Homework Equations
I reckon solving ##12345^{6789} mod(100)## would give the last two digits.
The Attempt at a Solution
I know that any number that ends with a 5 raised to any positive integer will end with a 5. I also know that the ten digit before the five and the exponent affects the outcome. Both being odd results in 75 as the last two digits and all other odd/even combinations of the two will result in 25 being the last two digits. But I cannot find information or a derivation of why this is the case.
Can someone help me on how to solve this congruence and maybe explain why those rules actually apply? I know the answer but I want to be able to present it with solid mathematics rather than "I read it online".
Thanks