\(a,A=\left(1+2\right)+\left(2^2+2^3\right)+...+\left(2^{10}+2^{11}\right)\\ A=\left(1+2\right)\left(1+2^2+...+2^{10}\right)=3\left(1+2^2+...+2^{10}\right)⋮3\\ b,B=\left(3+3^2+3^3\right)+...+\left(3^{58}+3^{59}+3^{60}\right)\\ B=3\left(1+3+3^2\right)+...+3^{58}\left(1+3+3^2\right)\\ B=\left(1+3+3^2\right)\left(3+...+3^{58}\right)=13\left(3+...+3^{58}\right)⋮13\\ c,M=\left(2+2^2+2^3+2^4\right)+...+\left(2^{17}+2^{18}+2^{19}+2^{20}\right)\\ M=2\left(1+2+2^2+2^3\right)+...+2^{17}\left(1+2+2^2+2^3\right)\\ M=\left(1+2+2^2+2^3\right)\left(2+...+2^{17}\right)=15\left(2+...+2^{17}\right)\\ M=5\cdot3\left(2+...+2^{17}\right)⋮5\)
