Help with average value of a function

credd741
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i have a question :cry:
how would you find a number b such that the average value of
f(x)= 1+10x-3x^2 on the interval [0,b] is equal to 4.

i have tried to set this equal to 4 but everytime i try to solve for b i get some number but it is always wrong. please help!:cry::cry::cry::cry:
 
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Welcome to the PF. How do you calculate the average of a function over an interval? What is the relevant equation?
 
the relevant equation is the f(x)=1+10x-3x^2
 
In order to find the average value of a function over a specified interval [0,b] you must integrate the function on that interval and divide by the interval length.

Can you formulate an equation which states these facts in terms of b and solve for b?
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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