Hello, jeilynn,

the slope m of a straight line between two points of this line is calculated by:1) slope (AB):Code:y1 - y2 m = ----------- x1 - x2

m_(AB) = (1 - (-1))/(-3 - 2) = 2/(-5) = -2/5

2) slope (BC):

m_(BC) = (-1 - 4)/(2 - 4) = (-5)/(-2) = 5/2

Because m_(Ab) * m_(BC) = -2/5 * 5/2 = -1 the lines (AB) is perpendicular to line (BC)