5.5 The Substitution Rule/67

Failed to parse (unknown function "\begin{align}"): {\displaystyle \begin{align}\int_{e}^{e^4}\frac{dx}{x\sqrt{lnx}}} &=$\int _{1}^{4}{\frac {1}{u}}du$ = $\int _{1}^{4}u^{-1/2}du$&=${\frac {u^{1/2}}{1/2}}{\bigg |}_{1}^{4}$ = ${2u}^{1/2}{\bigg |}_{1}^{4}$&=$2(4)^{1/2}-2(1)^{1/2}$&=Failed to parse (syntax error): {\displaystyle 2\end{align}}