Question 88301
Lets find the slope through (2, 3) and (11, 6) 


*[invoke slope 2, 3, 11, 6]



Lets find the slope through (2, 3) and (-3, 18) 


*[invoke slope 2, 3, -3, 18]



Now lets multiply the first slope {{{1/3}}} by {{{-3}}}. If the product equals -1, then they are perpendicular


{{{(1/3)(-3)=-3/3=-1}}}


Since the product between the two slopes is -1, this means they are perpendicular



Notice if we plot the points and draw lines between them, we get perpendicular lines


{{{drawing( 900, 900, -5, 20, -5, 20, 
         grid(1),
         circle(2,3,0.08),
         circle(2,3,0.10),
         circle(11,6,0.08),
         circle(11,6,0.10),

         circle(2,3,0.08),
         circle(2,3,0.10),
         circle(-3,18,0.08),
         circle(-3,18,0.10),


         line(2,3,11,6),
         line(2,3,-3,18)

)}}}