Question 1208150
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Let's calculate values of the slope in two intervals.


In the interval [0,1] of x-axis, the slope is  p = {{{delta_y/delta_x}}} = {{{(2-1)/(1-0)}}} = {{{1/1}}} = 1.


In the interval [1,2] of x-axis, the slope is  q = {{{delta_y/delta_x}}} = {{{(4-2)/(2-1)}}} = {{{2/1}}} = 2.



We see that the slopes are different.

Since the slopes at two intervals are different, it is just enough 
for us to conclude that the given function is nonlinear.
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At this point, the problem is solved in full, with complete explanations.