Considering the body of the task, a linear equation should be composed. In order to do that we have to find the slope coefficient of the line, that is, tangent of the slope angle. Sin angle = 9/10 - 4/10 = 1/2, cos angle = -1/5 - 2/5 = - 3/5, tan angle = -5/6. So f(x) = -(5/6)x
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