determine the following lines are parrallel ? x-y+1=0 6x-6y+7=0
$$\boxed{ \textcolor[rgb]{1,0,0}{a} *x + \textcolor[rgb]{0,0,1}{b} *y + c = 0 \qquad m = -\frac{ \textcolor[rgb]{1,0,0}{a} }{ \textcolor[rgb]{0,0,1}{b} } } \\$$
$$\\ \textcolor[rgb]{1,0,0}{1} *x \textcolor[rgb]{0,0,1}{-1} *y +1 = 0 \qquad m = -\frac{ \textcolor[rgb]{1,0,0}{1} }{ \textcolor[rgb]{0,0,1}{(-1)} } = 1
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\textcolor[rgb]{1,0,0}{6} *x \textcolor[rgb]{0,0,1}{-6} *y +7 = 0 \qquad m = -\frac{ \textcolor[rgb]{1,0,0}{6} }{ \textcolor[rgb]{0,0,1}{(-6)} } = 1 \\$$
The lines are parrallel because m is equal.