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29. What is the effect of doubling the interval length on the average rate of change of a linear function?

A. It quadruples the average rate of change.
B. It halves the average rate of change.
C. It has no effect on the average rate of change.
D. It doubles the average rate of change.

Sagot :

To understand the effect of doubling the interval length on the average rate of change of a linear function, let's analyze the concept of the average rate of change and how it applies to linear functions.

### Step-by-Step Solution:

1. Definition of Average Rate of Change:
The average rate of change of a function [tex]\( f(x) \)[/tex] over an interval [tex]\([a, b]\)[/tex] is given by:
[tex]\[ \text{Average Rate of Change} = \frac{f(b) - f(a)}{b - a} \][/tex]

2. Linear Function Properties:
For a linear function of the form [tex]\( f(x) = mx + c \)[/tex], where [tex]\( m \)[/tex] is the slope and [tex]\( c \)[/tex] is the y-intercept, the slope [tex]\( m \)[/tex] represents the rate of change. This slope is constant for any two distinct points on the linear function.

3. Impact of Changing the Interval:
Let's consider doubling the interval length. If the original interval is [tex]\([a, b]\)[/tex] with length [tex]\( b - a \)[/tex], doubling this interval gives us a new interval [tex]\([a, a + 2(b - a)]\)[/tex].
[tex]\[ \text{Original Interval Length} = b - a \][/tex]
[tex]\[ \text{New Interval Length} = 2(b - a) = b - a + (b - a) \][/tex]

4. Computing the Average Rate of Change for Original and New Intervals:
For the original interval [tex]\([a, b]\)[/tex], the average rate of change is:
[tex]\[ \text{Original Average Rate of Change} = \frac{f(b) - f(a)}{b - a} \][/tex]
Since [tex]\( f(x) = mx + c \)[/tex], we get [tex]\( f(b) = mb + c \)[/tex] and [tex]\( f(a) = ma + c \)[/tex], so:
[tex]\[ \text{Original Average Rate of Change} = \frac{mb + c - (ma + c)}{b - a} = \frac{mb - ma}{b - a} = \frac{m(b - a)}{b - a} = m \][/tex]

For the new interval [tex]\([a, a + 2(b - a)]\)[/tex], the average rate of change is:
[tex]\[ \text{New Average Rate of Change} = \frac{f(a + 2(b - a)) - f(a)}{(a + 2(b - a)) - a} \][/tex]
Again, using [tex]\( f(x) = mx + c \)[/tex], we have [tex]\( f(a + 2(b - a)) = m(a + 2(b - a)) + c \)[/tex]:
[tex]\[ \text{New Average Rate of Change} = \frac{m(a + 2(b - a)) + c - (ma + c)}{2(b - a)} \][/tex]
Simplifying the numerator, we get:
[tex]\[ \text{New Average Rate of Change} = \frac{ma + 2m(b - a) + c - ma - c}{2(b - a)} = \frac{2m(b - a)}{2(b - a)} = m \][/tex]

5. Conclusion:
Since the average rate of change [tex]\( m \)[/tex] remains the same regardless of the interval length, we can conclude that doubling the interval length has no effect on the average rate of change of a linear function.

Thus, the correct choice is:
- It has no effect on the average rate of change.

So, the answer is:

It has no effect on the average rate of change.