Question: ApproximateInt in function of the value cte, by example "a"

Hi, I try Aproximate integral with simpsons method, but i want value in function the a with number solution:

 

with(Student[Calculus1]);
ApproximateInt(a*tan(x)-2*x, x = -100 .. 100, method = simpson, output = plot, partition = 500);

This error.

 

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