Linear functions & quadrilaterals

In this applet we study the shape formed by two linear functions and the lines x = a and x = b. Use the white dots to set the values of a and b. Use the blue and green dots to determine the slopes of the two linear functions. What linear functions are the blue and green lines? Where do they intersect? What is area of the quadrilateral formed? [The user will notice that explorations with this applet are a superset of of those possible with the "Linear functions & yellow bowties" applet.]