algebra
posted by sharday .
1. Find the average rate of change of f(x)=x^39x+9:
a) from 8 to 2
b) from 1 to 1
c) from 1 to 4
a) what is averge rate of change of f (x) =x^39x+9 from 8 to 2?

algebra 
Reiny
I will do a) , you do the others in the same way
f(x) = x^3  9x + 9
f(2) = 8 + 18 + 9 = 19
f(8) = 512 + 72 + 9 = 431
avg rate of change
= (f(2)  f(8) )/(2  (8))
= (19  (431))/(2  (8))
=450/6
= 75
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