4) \;\;Given\;\; a \equiv 1 \pmod{7},\;\;and\;\; b \equiv 2 \pmod{7} \'\'and\;\; c \equiv 6 \pmod{7} \mbox { what is the remainder when } a^{81} b^{91} c^{27} \mbox{is divided by 7}\?
\(4) \;\;Given\;a \equiv 1 \pmod{7},\;\;and\; b \equiv 2 \pmod{7} \:and\;\; c \equiv 6 \pmod{7}\\ \mbox { what is the remainder when } a^{81} b^{91} c^{27}\; \mbox{is divided by 7}?\)
Thanks Heureka,
I have just finsihed Q4 too and I think our answers are fairly similar but I would like to post mine anyway :)
a=7p+1
b=7q+2
c=7r+6
p,q,r are integers
\(a^{81}=(7p+1)^{81}=1^{81}+81*(7p)^1+81C2*(7p)^2.........+(7p)^{81}\)
The only term here that is NOT a multiple of 7 is 1 and 1mod7=1
Using the same logic
\((7q+2)^{91}(mod 7) \\ =2^{91}(mod7)\\ =2^{10*9+1}(mod7) \\ =(2^{10})^{9}*2(mod7) \\ =(1024)^{9}*2(mod7) \\ =(2)^{9}*2(mod7) \\ =1*2(mod7) \\ =2(mod7) \)
and
\((7r+6)^{27}(mod7)\\ =6^{27}(mod7)\\ =((6^3)^3)^3(mod7)\\ =(216^3)^3(mod7)\\ =(6)^3(mod7)\\ =6(mod7)\)
so
\(a^{81} b^{91} c^{27} (mod7)\\ =1*2*6(mod7)\\ =12(mod(7)\\ =5 (mod7)\)
The remainder will be 5 Just like Heureka aready told us :)