Not sure if your the same person but I had already done the work for this problem....
If x^2+25y^2=416 and x-5y=-16 the value of xy is a)16 b)8 c)-8 d)-16
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The formula for the average value of a function is 
where b is the upper bound and a is the lower. For us, this formula will be filled in accordingly. 
. We will integrate that now: ![\frac{1}{2}[ \frac{2x^3}{3}+3x]](https://tex.z-dn.net/?f=%20%5Cfrac%7B1%7D%7B2%7D%5B%20%5Cfrac%7B2x%5E3%7D%7B3%7D%2B3x%5D%20%20)
from 0 to 2. Filling in our upper and lower bounds we have ![\frac{1}{2}[( \frac{2(2^3)}{3}+3(2))-0]](https://tex.z-dn.net/?f=%20%5Cfrac%7B1%7D%7B2%7D%5B%28%20%5Cfrac%7B2%282%5E3%29%7D%7B3%7D%2B3%282%29%29-0%5D%20%20)
which simplifies to 
and 
which is 17/3 or 5.667