Originally posted by Knight Square
This a very simple question. What is 2^2006, is the last digit 8? See I am a very stupid and dumb person so please if you do insult me, it just won't work. Okay I have already come to that reality, everybody has told me.
you can also work it out using modulo arithmetic. if we use modulo 10 then this says we're only looking at the last digit. 3*4=2 mod 10 as the last digit of 12 is 2. this holds for all natural numbers (and others, but that really doesn't matter here...)
2^2006 mod 10
=(2^2).(2^17).(2^59) (that's where long division-or a graphics calculator-come in handy...)
=4.(2^17).(2^59)
the last digit of 2^17 is 4 as we know that 18 is divisible by 3 and this the last digit of 2^18 is 8. 8/2=4. we can also work out 2^59 mod 10 this way.
thus,
2^2006 mod 10=4.4.4 mod 10=6.4 mod 10=4 mod 10.
this method is really kinda time-consuming here, but for other numbers it's more useful. i worked it all out then realised that actually it was a much simpler question and we didn't need mods. ThudanBlunder's method is simpler and easier (and quicker...) hereπ but i'd worked it all out, and spend a good 5 mins trying to remember how to do it all. so i decided not to let it all go to waste... π