a, \(\frac{1}{2}+x+1\frac{1}{2}=3\frac{3}{4}\)
\(\Rightarrow\frac{1}{2}+x+\frac{3}{2}=\frac{15}{4}\)
\(\Rightarrow\frac{1}{2}+\frac{3}{2}+x=\frac{15}{4}\)
\(\Rightarrow2+x=\frac{15}{4}\)
\(\Rightarrow x=\frac{15}{4}-2=\frac{7}{4}\)
Vậy : \(x=\frac{7}{4}\)
b, \(\frac{5}{6}\div x-\frac{4}{9}=\frac{3}{4}\)
\(\Rightarrow\frac{5}{6}\div x=\frac{3}{4}+\frac{4}{9}\)
\(\Rightarrow\frac{5}{6}\div x=\frac{27}{36}+\frac{16}{36}\)
\(\Rightarrow\frac{5}{6}\div x=\frac{33}{36}=\frac{11}{12}\)
\(\Rightarrow x=\frac{5}{6}\div\frac{11}{12}\)
\(\Rightarrow x=\frac{5}{6}.\frac{12}{11}\)
\(\Rightarrow x=\frac{10}{11}\)
Vậy : \(x=\frac{10}{11}\)