Question 975535
Distance formula between first and second, first and third, and second and third works.

first and second is sqrt(16+169)=sqrt (185)
second and third is sqrt (50)
first and third is sqrt (121+144)=sqrt (265)
This is not a right triangle.  This is proven by graphing as well, since no two lines are perpendicular, which they must be.

I reworked the slopes of all the lines, and they are 13/4, -1,7, and 12/11.  I can't find a negative reciprocal.


{{{graph(300,300,-10,10,-10,10,(13x/4)+6,(-x/7)+6,(12x/11)-(29/11))}}}