When asked for the area enclosed by three lines where one is the x-axis, y-axis, or parallel to an axis, do not split the shape or use integration. Use the axis-aligned segment as the base.
Trigger: 'enclose a region with area' or 'area of the shape bounded by', involving x=0, y=0, or x=c.
Instances:
(i) Triangle with a side on the y-axis: the base length is the difference between the y-intercepts of the other two lines.
(ii) The corresponding height is the absolute x-coordinate of the intersection of those two lines.
(iii) Trapezium bounded by x=a, x=b, y=0 and a slanted line: the parallel vertical sides are the heights of the slanted line at a and b, and the width is ∣b−a∣.
