The figure below shows a parallelogram ABCD. E is a point on AD and BD
intersects CE at F. If the area of triangle BCF is 9 and the area of
triangle EFD is 1, find the area of quadrilateral ABFE.
An isoline or contour line of a function of two variables is a curve along which the function has a constant value. Isolines usually have a parallel trend.
See also: Typography and poster of problem 1417.