avg value of cos x on interval [-3, 5]

[cocoachocobo]

The question asks for the avg value of cos x on interval [-3, 5]

okay, so for average value it would be
(1/8) (the integral from -3 to 5 of cos x)
which simplifies to
(1/8)(-sinx)from -3 to 5
simplifying that, i keep getting (-sin5 - sin3)/8

but its apparently just (sin5 + sin3) /8, where am i going wrong?

 

[skeeter]

The question asks for the avg value of cos x on interval [-3, 5]

okay, so for average value it would be
(1/8) (the integral from -3 to 5 of cos x)
which simplifies to
(1/8)(-sinx)from -3 to 5

antiderivative of cosx is sinx, not -sinx ...
[sin(5) - sin(-3)]/8 = [sin(5) - -sin(3)]/8 = [sin(5) + sin(3)]/8


simplifying that, i keep getting (-sin5 - sin3)/8

but its apparently just (sin5 + sin3) /8, where am i going wrong?