Hallo,
hier die hoffentlich richtige Lösung:
$$\vec{F_1}=3\;kN
\left(\begin{array}{c}
\cos(0\ensuremath{^\circ}})\\
\sin(0\ensuremath{^\circ}})\\
\end{array}\right)
=3\;kN
\left(\begin{array}{c}
1\\
0\\
\end{array}\right)$$
$$\vec{F_2}=5\;kN
\left(\begin{array}{c}
\cos(45\ensuremath{^\circ}})\\
\sin(45\ensuremath{^\circ}})\\
\end{array}\right)$$
$$\vec{F_3}=4\;kN
\left(\begin{array}{c}
-\cos(30\ensuremath{^\circ}})\\
-\sin(30\ensuremath{^\circ}})\\
\end{array}\right)
=-4\;kN
\left(\begin{array}{c}
\cos(30\ensuremath{^\circ}})\\
\sin(30\ensuremath{^\circ}})\\
\end{array}\right)$$
$$\vec{F_4}=2\;kN
\left(\begin{array}{c}
\cos(60\ensuremath{^\circ}})\\
-\sin(60\ensuremath{^\circ}})\\
\end{array}\right)$$
$$\vec{F}=\vec{F_1}+\vec{F_2}+\vec{F_3}+\vec{F_4}$$
$$\vec{F}=
\left(\begin{array}{c}
3\;kN+5\;kN\cos(45\ensuremath{^\circ}})-4\;kN\cos(30\ensuremath{^\circ}})+2\;kNcos(60\ensuremath{^\circ}})\\
0\;kN+5\;kN\sin(45\ensuremath{^\circ}})-4\;kN\sin(30\ensuremath{^\circ}})-2\;kN\sin(60\ensuremath{^\circ}})\\
\end{array}\right)$$
$$\sin(45\ensuremath{^\circ}})=\cos(45\ensuremath{^\circ}})=\frac{\sqrt{2}}{2}$$
$$\sin(30\ensuremath{^\circ}})=\frac{1}{2}\quad\cos(30\ensuremath{^\circ}})=\frac{\sqrt{3}}{2}\quad\sin(60\ensuremath{^\circ}})=\frac{\sqrt{3}}{2}\quad\cos(60\ensuremath{^\circ}})=\frac{1}{2}$$
$$\vec{F}=
\left(\begin{array}{c}
3\;kN+\frac{5}{2}\sqrt{2}\;kN-2\sqrt{3}\;kN+1\;kN\\
\frac{5}{2}\sqrt{2}\;kN-2\;kN-\sqrt{3}\;kN\\
\end{array}\right)=
\left(\begin{array}{c}
4,07143229079\;kN\\
-0,19651690164\;kN\\
\end{array}\right)$$
$$\textcolor[rgb]{1,0,0}{R=}|\vec{F}|=\sqrt{4,07143229079^2+(-0,19651690164)^2} = \textcolor[rgb]{1,0,0}{4,07617219842\;kN}$$
$$\textcolor[rgb]{1,0,0}{\theta=}\arctan(\frac{-0,19651690164}{4,07143229079})+360\ensuremath{^\circ}=-2\stackrel{\ensuremath{^\circ}}{,}76336594484+360\ensuremath{^\circ}=\textcolor[rgb]{1,0,0}{357\stackrel{\ensuremath{^\circ}}{,}236634055}$$
Die rerultierende R hat die Größe $$\textcolor[rgb]{1,0,0}{4,076\;kN}$$mit einem Winkel $$\textcolor[rgb]{1,0,0}{\theta=357\stackrel{\ensuremath{^\circ}}{,}24}$$
S. aus. H.