We can see that
[tex]\angle2+\angle3\text{ =180\degree}[/tex]since they are on a straight line. Likewise,
[tex]\angle3+\angle4=180\degree[/tex]We now have the equation
[tex]\angle2+\angle3=\angle3+\angle4[/tex]Substracting from both sides of the equation we get
[tex]\angle2+\angle3-\angle3=\angle3+\angle4-\angle3[/tex]And thus
[tex]\angle2=\angle4[/tex]
