Question 1199965
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The maximum is reached when   cos(x) = 0  and  sin(x) = 1.


It happens at   x = {{{pi/2}}}.


The value of the maximum is  &nbsp;&nbsp;13 + 6*1 - 9*0 = 13 + 6 = 19.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<U>ANSWER</U>


Solved.


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My statements are obviously true even without any calculations/transformations.