[tex]\displaystyle\bf\\6^{\bigstar}.\\a)\\\\\Big(5^{17}\cdot5^{18}+7^{23}:7^{15}\Big):\Big(7\cdot7^2\cdot7^5+5^{50}:5^{15}\Big)=\\\\\\=\frac{5^{17}\cdot5^{18}+7^{23}:7^{15}}{7\cdot7^2\cdot7^5+5^{50}:5^{15}}=\\\\\\=\frac{5^{17+18}+7^{23-15}}{7^{1+2+5}+5^{50-15}}=\\\\\\=\frac{5^{35}+7^{8}}{7^{8}+5^{35}}=\frac{5^{35}+7^{8}}{5^{35}+7^{8}}=\boxed{\bf1}~~deoarece~numaratorul=numitorul.[/tex]
