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And you know as well that to every function corresponds its graph. But on the graphical side, the addition of functions may apear harder, as you no longer have obvious means to compute.
This is precisely what this exercise proposes: you will be given graphs of functions, and asked to find back the coefficients of the combinations leading to these graphs. Like many other exercises on WIMS, training by this exercise will allow you to increase you ability to graphically recognize functions.