Answer: Choice A -- f(x) = (1/3)*|x|
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The input of a function is x and the output is y = f(x)
To vertically compress a function, we will multiply the y value by some fraction smaller than 1. This is so that the y coordinates are a fraction of what they once were.
In this case, we multiply y by 1/3 so that something that has a y coordinate of y = 81 becomes y = 27 (divide by 3)
So we have y = f(x) become (1/3)*y = (1/3)*f(x) = (1/3)*|x|