\documentclass[10pt,letterpaper,fleqn]{scrbook} \usepackage[left=3cm,right=2.5cm,top=2.5cm,bottom=2.5cm, marginparwidth=2.85cm, marginparsep=0pt]{geometry} \usepackage[leqno]{mathtools} \newtagform{bold}{}{\textbf{)}} \usetagform{bold} \renewcommand*{\theequation}{\textbf{Ej. 1.}} \newcommand{\remark}[1]{& \quad \longleftarrow & \quad\fontsize{8}{0}\selectfont\parbox{0.25\textwidth}{\raggedright#1}} \setlength{\jot}{10pt} \begin{document} \begin{equation} \begin{alignedat}[t]{2} \int \frac{x^2 + x + 1}{\sqrt{x}}\,dx &= \int \frac{x^2}{\sqrt{x}}\,dx + \int \frac{x}{\sqrt{x}}\,dx + \int \frac{1}{\sqrt{x}}\,dx \remark{separar en 3 integrales} \\ &= \int \frac{x^2}{x^{1/2}}\,dx + \int \frac{x}{x^{1/2}}\,dx + \int \frac{1}{x^{1/2}}\,dx \remark{escribir los radicales en forma de potencia} \\ &= \int x^{3/2}\,dx + \int x^{1/2}\,dx + \int x^{- 1/2}\,dx \remark{reescribir} \\ &= \frac{x^{5/2}}{5/2} + \frac{x^{3/2}}{3/2} + \frac{x^{1/2}}{1/2} + C \remark{integrar} \\ &= \frac{2}{5}\,x^{5/2} + \frac{2}{3}\,x^{3/2} + 2\,\sqrt{x} + \remark{simplificar} \end{alignedat} \end{equation} \end{document}
produces the following result in the attached picture, the
bf
text must to be left-aligned in the first line, I don't know what's wrong here...this is the recommendation you gave me to align the equations!