Question

Find the average rate of change of f ( x ) = 3 x 2 − 9 on the interval [ 2 , b ] . Your answer will be an expression involving b

Answer 1

Answer:

$m = 3b+6$

Step-by-step explanation:

Given

$f(x)=3x^2 - 9$

Required

The average rate over $[2,b]$

Average rate (m) is calculated using:

$m = \frac{f(b) - f(a)}{b - a}$

Where

$[a,b] = [2,b]$

So, we have:

$m = \frac{f(b) - f(2)}{b - 2}$

Calculate f(b) and f(2)

$f(x)=3x^2 - 9$

$f(b)=3b^2 - 9$

$f(2)=3*2^2 - 9 = 12 - 9 = 3$

So, we have:

$m = \frac{f(b) - f(2)}{b - 2}$

$m = \frac{3b^2 - 9 - 3}{b - 2}$

$m = \frac{3b^2 - 12}{b - 2}$

Expand the numerator

$m = \frac{3b^2 + 6b-6b-12}{b - 2}$

Factorize

$m = \frac{b(3b + 6)-2(3b+6)}{b - 2}$

Factor out 3b + 6

$m = \frac{(b -2)(3b+6)}{b - 2}$

Cancel out b - 2

$m = 3b+6$