Jeff wants to save $4000 to buy a used car. He has already saved $850. He plans to save an additional $150 each week. write and
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Answer:
(a) The function is increasing and decreasing
(b) The local minimum is x = 5 and the maximum is x = -6
(c) The inflection point is
(d) The function is concave upward on and concave downward on
Step-by-step explanation:
(a) To find the intervals where is increasing or decreasing you must:
1. Differentiate the function
2. Now we want to find the intervals where f'(x) is positive or negative. This is done using critical points, which are the points where f'(x) is either 0 or undefined.
These points divide the number line into three intervals:
,
, and
Evaluate f'(x) at each interval to see if it's positive or negative on that interval.
Therefore f(x) is increasing and decreasing
(b) Now that we know the intervals where f(x) increases or decreases, we can find its extremum points. An extremum point would be a point where f(x) is defined and f'(x) changes signs.
We know that:
- f(x) increases before x = -6, decreases after it, and is defined at x = -6. So f(x) has a relative maximum point at x = -6.
- f(x) decreases before x = 5, increases after it, and is defined at x = 5. So f(x) has a relative minimum point at x = 5.
(c)-(d) An Inflection Point is where a curve changes from Concave upward to Concave downward (or vice versa).
Concave upward is when the slope increases and concave downward is when the slope decreases.
To find the inflection points of f(x), we need to use the f''(x)
We set f''(x) = 0
Analyzing concavity, we get
The function is concave upward on because the f''(x) > 0 and concave downward on
because the f''(x) < 0.
f(x) is concave down before , concave up after it. So f(x) has an inflection point at
.