   \begin{tabular}{cc}
    \begin{tikzpicture}%
    	[x={(240:2cm)},
    	y={(0:2cm)},
    	z={(120:2cm)},
        scale=0.4]
    
    \coordinate (0) at (0,0,0);
    \coordinate (w1) at (3,0,0);    
    \coordinate (w2) at (0,3,0);    
    \coordinate (w3) at (0,0,3);    
    \coordinate (-w1) at (-3,0,0);
    \coordinate (-w2) at (0,-3,0);    
    \coordinate (-w3) at (0,0,-3);   

    \coordinate (alpha1) at (-1,1,0);
    \coordinate (alpha2) at (0,-1,1);
    
     \draw (0) -- (w1);
     \draw (0) -- (w2);
     \draw (0) -- (w3);
     \draw (0) -- (-w1);
     \draw (0) -- (-w2);
     \draw (0) -- (-w3);
    
     \node[left] at (w3) {$x_2-x_1=0$};
     \node[right] at (-w1) {$x_3-x_2=0$};
     \node[right] at (w2) {$x_3-x_1=0$}; 

    \end{tikzpicture}  
    &
    \quad
    \begin{tikzpicture}
        	[x={(240:2cm)},
    	y={(0:2cm)},
    	z={(120:2cm)},
        scale=0.4]

    \coordinate (0) at (0,0,0);
    \coordinate (w1) at (3,0,0);    
    \coordinate (w2) at (0,3,0);    
    \coordinate (w3) at (0,0,3);    
    \coordinate (-w1) at (-3,0,0);
    \coordinate (-w2) at (0,-3,0);    
    \coordinate (-w3) at (0,0,-3);   

     \draw[dashed] (0) -- (w1);
     \draw[dashed] (0) -- (w2);
     \draw[dashed] (0) -- (w3);
     \draw[dashed] (0) -- (-w1);
     \draw[dashed] (0) -- (-w2);
     \draw[dashed] (0) -- (-w3);

    \coordinate (alpha1) at (-1,1,0);
    \coordinate (alpha2) at (0,-1,1);  
    \coordinate (alpha12) at ($(alpha1)+(alpha2)$);
    \coordinate (minusalpha1) at ($-1*(alpha1)$);
    \coordinate (minusalpha2) at ($-1*(alpha2)$);  
    \coordinate (minusalpha12) at ($-1*(alpha1)-1*(alpha2)$);

    \draw[->] (0) -- (alpha1);
    \draw[->] (0) -- (alpha2);
    \draw[->] (0) -- (alpha12);
    \draw[->] (0) -- (minusalpha1);
    \draw[->] (0) -- (minusalpha2);
    \draw[->] (0) -- (minusalpha12);

    \node[right] at (alpha1) {$\alpha_1$};    
    \node[left] at (alpha2) {$\alpha_2$};    
    \node[above] at (alpha12) {$\alpha_1+\alpha_2$};    
    \node[right] at (minusalpha2) {$-\alpha_2$};    
    \node[left] at (minusalpha1) {$-\alpha_1$};    
    \node[below] at (minusalpha12) {$-\alpha_1-\alpha_2$};    
    \end{tikzpicture}
    \end{tabular}