85. The complex function $y=\sin u$, where $u=\lg v, v=\sqrt{x}$, write as a single equation.
Solution. Substituting the value $v=\sqrt{x}$ into the equation $u=\lg v$, we get $u=\lg \sqrt{x}$. Next, substituting the obtained value for $u$ into the equation $y=\sin u$; then the given composite function will take the form $y=$ $=\sin (\lg \sqrt{x})$.