we can use formula
[tex]\theta=tan^{-1}(\frac{a_y}{a_x})[/tex]
(a)
we are given
[tex]a_x=12,a_y=12[/tex]
now, we can plug values
[tex]\theta=tan^{-1}(\frac{12}{12})[/tex]
[tex]\theta=tan^{-1}(1)[/tex]
[tex]\theta=\frac{\pi}{4}rad [/tex]
(b)
we are given
[tex]a_x=20,a_y=12[/tex]
now, we can plug values
[tex]\theta=tan^{-1}(\frac{12}{20})[/tex]
[tex]\theta=tan^{-1}(\frac{3}{5})[/tex]
[tex]\theta=30.96^{\circ \:} [/tex]
(c)
we are given
[tex]a_x=12,a_y=20[/tex]
now, we can plug values
[tex]\theta=tan^{-1}(\frac{20}{12})[/tex]
[tex]\theta=tan^{-1}(\frac{5}{3})[/tex]
[tex]\theta=59.03^{\circ \:} [/tex]