The slope of a relationship is the change in the value of
the variable on the y-axis divided by the change in the
value of the variable on the x-axis. The formula for
slope is Δy/Δx, with Δ meaning “change in.”
A straight line (or linear relationship) has a constant
slope. A curved line has a varying slope, which can be
calculated two ways:
♦ Slope at a point — by drawing the straight line tangent
to the curve at that point and then calculating
the slope of the line.
♦ Slope across an arc — by drawing a straight line
across the two points on the curve and then calculating
the slope of the line.