Answer:
the slope of the tangent line at (40, f(40))the slope of the tangent line at (15, f(15)) the slope of the tangent line at (10, f(10))the slope of the line segment from (10, f(10)) to (40, f(40))
Answer:
is sometimes positive and sometimes negative.
Step-by-step explanation:

Take 

Take 

Hence
for
and
for 
So
is sometimes positive and sometimes negative in the interval.
Answer:
To find the sales tax multiply the purchase price by the sales tax rate. Remember to convert the sales tax rate from a percent to a decimal number. Once the sales tax is calculated, it is added to the purchase price. The result is the total cost—this is what the customer pays.
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Solving Sales Tax