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Autumn tournament

Bulgaria geometry

Problem

Given the functions and . Find the area of the figure with vertices, the intersection points of the graphs of the functions and and the intersection points of the graph of with the x-axis. (Nedyalka Dimitrova)
Solution
The graph of consists of two rays with a common vertex at . We remove the module and easily calculate its intersection points with the x-axis through the equations and and .

After removing the modules in we see that in the interval , in the interval and in the interval . We solve the equations for each of the three intervals. We get the following intersection points — and .

It follows that the figure is a trapezoid with bases and and height . Therefore, its area is .
Final answer
12

Techniques

Cartesian coordinates