Bestäm vinkeln

Tänkte så här

$$\begin{gathered} \frac{v_{0x}}{\cos \left(a\right)}=v_0 \\ {v}_{0y}=\frac{v_{0x}*\sin \left(a\right)}{\cos \left(a\right)} \\ 0 =\hspace{0.17em}\frac{58,3 \sin \left(a\right)}{\cos \left(a\right)}-gt (58,3 är hastigheten i x-led i m/s) \\ t=\hspace{0.17em}\frac{58,3 \sin \left(a\right)}{\cos \left(a\right)g} \\ t =\hspace{0.17em}\frac{5,9 \sin \left(a\right)}{\cos \left(a\right)}=5,9\tan \left(a\right) \\ -110 =\hspace{0.17em}\frac{v_{0x}\sin {\left(a\right)}^{2}5,9}{\cos {\left(a\right)}^2}-\frac{171\sin {\left(a\right)}^2}{\cos {\left(a\right)}^2}=173\tan {\left(a\right)}^2 \\ -110 =\hspace{0.17em}\frac{344\sin {\left(a\right)}^2}{\cos {\left(a\right)}^2}-\frac{171\sin {\left(a\right)}^2}{\cos {\left(a\right)}^2}=173\tan {\left(a\right)}^2 \\ -110 =173\tan {\left(a\right)}^2 \end{gathered}$$

Men kommer inte vidare då jag får roten ur ett negativt tal