Question 438202
{{{V[1]}}} = <-1-2, -1-0> = <-3, -1>
{{{V[2]}}} = <1--1, 3--1> = <2, 4>
{{{V[3]}}}= <1-2, 3-0> = <-1, 3>

Take dot products:
{{{V[1]*V[2] = -6 - 4 = -10}}}
{{{V[2]*V[3] = -2 + 12 = 10}}}
{{{V[1]*V[3] = 3 - 3 = 0}}}
==> the sides of the triangle, {{{V[1]}}} and {{{V[3]}}} are perpendicular, and so  the triangle is a right triangle.