college algebra (average rate of change)
posted by Brianna .
If the average rate of change of g(x) from x = 1 to x = 9 is 20, and if the average rate of change of g(x) from x = 9 to x = 21 is 40, then what is the average rate of change of g(x) from x = 1 to x = 21?

from 1 to 9, g(x) = 20(x1)
so, g(9) = g(1) + 160
similarly, g(21) = g(9) + 40(219)
= g(9) + 480
So, g(21) = g(1) + 160 + 480 = g(1)+640
640/(211) = 640/20 = 32
The average rate of change from x=1 to 21 is 32. 
solve using the graphing method y=x3
y=1/2x=3