[tex]\text{a)} \\ \\ S\,\,\,= 2^0+2^1+2^2+2^3+...+2^{50}\\2S =\quad\,\,\,\,\,\,\,2^1+2^2+2^3+...+2^{50}+2^{51} \\ \noindent\rule{6.2cm}{0.7pt}\\ \\2S - S = 2^{51} +2^{50}+2^{49}+...+2^{1} - (2^{50}+2^{49}+{\dots}+2^{1} )-2^0\\\\S = 2^{51} - 2^0 \\ \\\Rightarrow S = 2^{51} - 1\\ \\ \\ \text{b)}\\ \\ 1+2+4+8+...+2^n=1023 \\ \\ 2^0 + 2^1 + 2^2 + 2^3 + ... + 2^n = 1023 \\ \\ 2^{n+1}-1 = 1023 \\ \\ 2^{n+1} = 1024\\ \\ 2^{n+1} = 2^{10}\\ \\ n+1 = 10 \\ \\ \Rightarrow n = 9\\ \\ R\u{a}spuns:\,\,\,9\text{ zile}.[/tex]