Question 110696
I'm going to assume that you meant point (2,3) for the first point of line A since '#' is Shift-3.
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Step 1 is to calculate the slopes of each line:
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{{{m[A]=(21-3)/(-4-2)=18/-6=-3}}}, and
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{{{m[B]=(1-(-1))/(10-4)=2/6=1/3}}}
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Line A is parallel to line B if and only if {{{m[A]=m[B]}}}, but {{{-3<>1/3}}} so line A is NOT parallel to line B.
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Line A is perpendicular to line B if and only if {{{m[A]=-1/m[B]}}}.  Since {{{-3=(-1)/(1/3)}}}, line A IS perpendicular to line B.
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And they look perpendicular to me.
{{{graph(400,400,0,6,-3,3,(-3)x+9,(1/3)x-(7/3))}}}
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Extra credit:  Write back and tell me which line, red or green, is Line A.