a) \(A=\dfrac{-45.58-45.42}{2+4+6+...+16+18}\)
\(A=-\dfrac{45\left(58+42\right)}{\dfrac{\left(18-2\right):2+1}{2}.\left(2+18\right)}\)
\(A=\dfrac{-45.100}{\dfrac{5}{2}.20}\)
\(A=-\dfrac{45.100}{50}\)
\(A=-90\)
b) \(1-\left[\left(5\dfrac{3}{8}+x-7\dfrac{5}{24}\right):\left(-16\dfrac{2}{3}\right)\right]=0\)
\(\Rightarrow\left(5\dfrac{3}{8}+x-7\dfrac{5}{24}\right):\left(-16\dfrac{2}{3}\right)=1\)
\(\Rightarrow\left(\dfrac{43}{8}+x-\dfrac{173}{24}\right):\left(-\dfrac{46}{3}\right)=1\)
\(\Rightarrow\left(\dfrac{129}{24}-\dfrac{173}{24}+x\right).\left(-\dfrac{3}{46}\right)=1\)
\(\Rightarrow\left(-\dfrac{44}{24}+x\right).\left(-\dfrac{3}{46}\right)=1\)
\(\Rightarrow\left(-\dfrac{11}{6}+x\right).\left(-\dfrac{3}{46}\right)=1\)
\(\Rightarrow-\dfrac{11}{6}+x=1.\left(-\dfrac{46}{3}\right)\)
\(\Rightarrow-\dfrac{11}{6}+x=-\dfrac{46}{3}\)
\(\Rightarrow x=-\dfrac{46}{3}+\dfrac{11}{6}\)
\(\Rightarrow x=-\dfrac{92}{6}+\dfrac{11}{6}\)
\(\Rightarrow x=-\dfrac{81}{6}\)
\(\Rightarrow x=-\dfrac{27}{2}\)