The sides of a square are perpendicular.
The slope of BC is perpendicular to AB. So let us find the slope of AB first.
[tex] = \frac{ - 3 - 2}{3 - 1} [/tex]
[tex] = \frac{ - 5}{2} [/tex]
Slope of AB × Slope of BC = -1
[tex] - \frac{ 5}{2} \times slope \: of \: bc = - 1[/tex]
Slope of BC
[tex] = - \frac{ - 1}{ - \frac{5}{2} } [/tex]
[tex] = - 1 \times \frac{ - 2}{5} [/tex]
[tex] = \frac{2}{5} [/tex]
Hence the slope of BC is
[tex] \frac{2}{5} [/tex]
