Let's write the equation system first. We have two angles, let's call the, A and B, wich are complementary. This is:
[tex]A+B=90º[/tex]Also their difference is 40º:
[tex]A-B=40º[/tex]The system is;
[tex]\begin{cases}A+B=90º \\ A-B=40º\end{cases}[/tex]Now, if we add the two equations, since we have a "B" and a "-B", they will eliminate:
[tex]\begin{gathered} (A+B=90º)+(A-B=40º) \\ A+B+A-B=90º+40º \\ A+A+B-B=130º \\ 2A=130º \\ A=\frac{130º}{2}=65º \end{gathered}[/tex]The value of one of the angles is 65º. To find the other angle, we can go back to the first equation, A + B = 90º:
[tex]65º+B=90º[/tex]And solve:
[tex]B=90º-65º=25º[/tex]The larger angle is 65º and the smaller angle is 25º