debate math problems.?

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Phan A

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The average value of the function f(x)=cos(x/2) on the closed interval[-4,0] is what?
My answer is -1/2sin(2) and I find another answer which is 1/2sin(2). ( no negative )
Please if you could figure this out... If there is a negative. THank you in advance.
 
int from -4 to 0 of cos(x/2)
= 2sin(x/2)
=2sin(0)-(2sin(-4/2))
=0-2sin(-2)=-(-2sin(2)),
since sin is an odd function, sin(-x)=-sin(x)
=2sin(2)
therefore the average value is: 2sin(2)/4=1/2sin(2)
 
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