\(A=2^2+2^3+.......2^{60}\)
\(A=\left(2+2^2\right)+\left(2^3+2^4\right)+\left(2^5+2^6\right)+........\left(2^{59}+2^{60}\right)\)
\(A=2.\left(1+2\right)+2^3.\left(1+2\right)+......2^{59}.\left(1+2\right)\)
\(A=2.3+2^3.3+....2^{59}.3\)
\(A=3.\left(2+2^3+...2^{59}\right)\)
\(\Rightarrow A⋮3\)
\(\text{Tìm x,y thuộc N biết:
(41-2.x).(2.y-7)=21}\)
\(\left(41-2.x\right)=21\)
\(\Rightarrow2.x=41-21\)
\(\Rightarrow2.x=20\)
\(\Rightarrow x=20:2\)
\(\Rightarrow x=10\)
\(2.y-7=21\)
\(\Rightarrow2.y=21+7\)
\(\Rightarrow2.y=28\)
\(\Rightarrow y=28:2\)
\(\Rightarrow y=16\)
Vậy x = 10 y =16
