We are given coordinates of A, B, C and D :
A(2, 4), B(9, 8), C(-1, 2), and D(3, -5).
Now, we need to find the slopes of AB and CD.
Slope of AB is :
.
Slope of CD is:
.
<em>Slope of CD is negative reciprocal of slope of slope of AB. </em>
<h3>Therefore, lines AB are CD are perpendicular.</h3>