Step-by-step explanation:
[tex] \sin \: \phi = \cos( \phi + 20 \degree) \\ \\ \therefore \: \cos (90 \degree - \phi )= \cos( \phi + 20 \degree) \\ \\ \therefore \: 90 \degree - \phi = \phi + 20 \degree \\ \\ \therefore \: 90 \degree - 20 \degree = \phi +\phi \\ \\ \therefore \: 70 \degree = 2\phi \\ \\ \therefore \: \phi = \frac{70 \degree}{2} \\ \\ \huge \red { \boxed{ \therefore \: \phi = 35 \degree}}[/tex]
