[tex] \alpha + \beta = 90[/tex]
[tex] \beta + 4 \alpha = 180[/tex]
Multiply the upper system by -1:
[tex] - \alpha - \beta = - 90[/tex]
[tex] \beta + 4 \alpha = 180[/tex]
Add the systems:
[tex]3 \alpha = 90[/tex]
[tex] \alpha = 30[/tex]
[tex] \beta = 90 - \alpha = 90 - 30 = 60[/tex]
[tex]( \alpha = 30) < = > ( \beta = 60)[/tex]
