[tex]\it a)\ d_1:\ \ x-y-1=0 \Rightarrow y=x-1 \Rightarrow m_{d_1}=1\\ \\ d_2:\ \ x+y-1=0 \Rightarrow y=-x+1 \Rightarrow m_{d_2}=-1\\ \\ m_{d_1}\cdot m_{d_2} =-1 \Rightarrow d_1\perp d_2[/tex]
[tex]\it b)\ d_1:\ \ 2x-y=3 \Rightarrow y=2x-3 \Rightarrow m_{d_1}=2\\ \\ d_2:\ \ x-3y=2 \Rightarrow 3y=x-2 \Rightarrow y=\dfrac{1}{3}x-\dfrac{2}{3} \Rightarrow m_{d_2}=\dfrac{1}{3}\\ \\ m_{d_1}\ne m_{d_2}\ \ \c{s}i\ \ m_{d_1}\cdot m_{d_2}\ne -1 \Rightarrow d_1,\ d_2\ sunt\ concurente\ (neperpendiculare)[/tex]
