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Which expression represents the difference quotient of the function [tex]f(x) = \frac{13 - 5x}{4}[/tex] for all nonzero values of [tex]h[/tex]?

A. [tex]\frac{1}{4}[/tex]
B. [tex]\frac{h}{4}[/tex]
C. [tex]-\frac{5}{4}[/tex]
D. [tex]-\frac{5h}{4}[/tex]


Sagot :

To find the difference quotient of the function [tex]\( f(x) = \frac{13 - 5x}{4} \)[/tex] for all nonzero values of [tex]\( h \)[/tex], we will follow these steps:

1. Write the difference quotient formula:
The difference quotient [tex]\( \frac{f(x+h) - f(x)}{h} \)[/tex] measures the average rate of change of the function [tex]\( f(x) \)[/tex] over an interval of width [tex]\( h \)[/tex].

2. Substitute [tex]\( f(x) \)[/tex] and [tex]\( f(x+h) \)[/tex] into the difference quotient:
Given [tex]\( f(x) = \frac{13 - 5x}{4} \)[/tex], we first need to find [tex]\( f(x + h) \)[/tex].

[tex]\[ f(x + h) = \frac{13 - 5(x + h)}{4} \][/tex]

3. Simplify [tex]\( f(x + h) \)[/tex]:

[tex]\[ f(x + h) = \frac{13 - 5x - 5h}{4} \][/tex]

4. Form the difference quotient using [tex]\( f(x + h) \)[/tex] and [tex]\( f(x) \)[/tex]:

[tex]\[ \frac{f(x + h) - f(x)}{h} = \frac{\frac{13 - 5x - 5h}{4} - \frac{13 - 5x}{4}}{h} \][/tex]

5. Combine the fractions in the numerator:

[tex]\[ \frac{\frac{13 - 5x - 5h}{4} - \frac{13 - 5x}{4}}{h} = \frac{\frac{(13 - 5x - 5h) - (13 - 5x)}{4}}{h} = \frac{\frac{13 - 5x - 5h - 13 + 5x}{4}}{h} \][/tex]

6. Simplify the numerator:

[tex]\[ \frac{\frac{13 - 5x - 5h - 13 + 5x}{4}}{h} = \frac{\frac{-5h}{4}}{h} \][/tex]

7. Divide by [tex]\( h \)[/tex]:

[tex]\[ \frac{\frac{-5h}{4}}{h} = \frac{-5h}{4h} = \frac{-5}{4} \][/tex]

So, the difference quotient simplifies to [tex]\( -\frac{5}{4} \)[/tex].

Therefore, the correct expression representing the difference quotient of the function [tex]\( f(x)=\frac{13-5x}{4} \)[/tex] for all nonzero values of [tex]\( h \)[/tex] is:

[tex]\[ -\frac{5}{4} \][/tex]

Thus, the correct answer is:

[tex]\[ -\frac{5}{4} \][/tex]