Increasing, Decreasing, Maxima and Minima

From the graph of the function $f(x)$ below, determine the intervals where the function is strictly increasing and where it is strictly decreasing.

Sketch a continuous graph in your notebook whose domain is all of $\mathbb{R}$, which is strictly increasing in the intervals $(-\infty, -2)$ and $(3, +\infty)$, and strictly decreasing in the interval $(-2, 3)$. Based on your sketch, what type of local extrema (maximum or minimum) will occur at the x-coordinates $x = -2$ and $x = 3$?

You can do it on paper and send a photo with your answer.

Look at the graph of the function $g(x)$ and write down the exact coordinates of the points labelled A, B and C. State whether each point is a local maximum or local minimum. Are any of these turning points also absolute extrema on the domain shown?

Sketch a continuous function $f(x)$ in your notebook that satisfies all of the following conditions simultaneously:

• Its domain is the interval $[-5, 6]$.

• Its range is the interval $[-2, 5]$.

• It is strictly increasing in $[-5, -1] \cup [3, 6]$ and strictly decreasing in $[-1, 3]$.

• It passes through the points $(-1, 5)$ and $(3, -2)$.

What do the points $(-1, 5)$ and $(3, -2)$ represent mathematically on the graph of this function?

The following graph corresponds to a degree 4 polynomial function, $f(x)$, which has a W-shape. By observing the graph, estimate the coordinates of its local extrema (maximums and minimums). Next, knowing that the function is perfectly symmetrical with respect to the y-axis (it is an even function), reason and prove whether the average rate of change in the symmetric interval $[-3, 3]$ will be positive, negative, or zero.

Calculate the average rate of change of the linear function $f(x) = 4x - 7$ in the interval $[-2, 3]$. Based on your result, what can you deduce about whether the function is increasing or decreasing in this interval?

The following table of values shows the altitude $h$ (in metres) of a weather balloon as a function of time $t$ (in seconds) since launch.

Calculate the average rate of change in the intervals $[0, 2]$ and $[4, 6]$. Based on these results, is the altitude function increasing or decreasing over these intervals?

Consider the function $f(x) = x^2 - 9$. Calculate the average rate of change in the interval $[-4, -1]$ and in the interval $[1, 4]$. Relate the sign of each result to the behaviour (increasing or decreasing) of the function over these two intervals.

Given the inverse proportion function $f(x) = \frac{12}{x}$, calculate the average rate of change in the intervals $[1, 3]$ and $[3, 6]$. Verify that, although the numerical values of the average rate of change are different in each interval, both results confirm the decreasing behaviour of the function in the interval $(0, +\infty)$.

Given the quadratic function $f(x) = -3x^2 + 12x - 5$, state, without plotting the graph or calculating its coordinates, whether the vertex of the parabola corresponds to a local maximum or a local minimum. Justify your answer by looking at the signs of the coefficients of the function.

The height $h$ (in metres) reached by a fireworks rocket as a function of time $t$ (in seconds) since launch is given by the expression $h(t) = -5t^2 + 40t + 2$. Calculate the exact time at which the rocket reaches its maximum height and the exact value of this height.

The number of individuals $N$ in an insect population in a laboratory experiment varies with the number of days $t$ elapsed according to the quadratic model $N(t) = 3t^2 - 24t + 150$, valid for $t \ge 0$. Determine on which day the insect population reaches its minimum size and how many individuals make up the population at that exact moment.

A total of $60$ metres of metal fencing is available to enclose a rectangular vegetable garden against the straight wall of a barn, so only three sides need fencing. If $x$ is the length of the two sides perpendicular to the barn wall, find the quadratic function $A(x)$ that expresses the area of the garden in terms of $x$. What must be the exact dimensions of the garden for its area to be as large as possible?

Determine with justification the algebraic expression of a quadratic polynomial function $f(x) = ax^2 + bx + c$ that simultaneously satisfies three conditions: 1) it has an absolute extremum at the point $V(2, 5)$; 2) it is strictly increasing on the interval $(-\infty, 2)$ and strictly decreasing on $(2, +\infty)$; 3) it intersects the y-axis at the point $(0, 1)$. Justify how you deduce the sign of the leading coefficient $a$, how you use the vertex formula or the vertex form of the parabola to set up the necessary equations, and find the exact values of the coefficients $a$, $b$, and $c$.

The temperature of an industrial oven starts at $20 \ ^\circ\text{C}$. During the first $15$ minutes it rises uniformly until reaching $220 \ ^\circ\text{C}$. It remains at this constant temperature for $45$ minutes to bake some parts, and is then switched off, with the temperature falling uniformly to $20 \ ^\circ\text{C}$ over $30$ minutes. State the time intervals over which the temperature is increasing, decreasing, and constant, as well as the absolute maximum value reached by the function.

The accompanying graph represents the speed $v$ (in km/h) of a vehicle along a journey as a function of time $t$ (in minutes). State the time intervals over which the vehicle accelerates (increasing speed), decelerates (decreasing speed), or maintains a constant speed. What is the maximum speed reached during the journey and for how long is it maintained?

The fuel consumption $C(v)$ (in liters per $100\text{ km}$) of a passenger car driving on a highway at a constant speed $v$ (in $\text{km}/\text{h}$, for $60 \le v \le 140$) is modeled by the quadratic function $C(v) = 0.001v^2 - 0.18v + 12.6$. a) Model the most economical driving: calculate at what cruising speed fuel consumption is minimal and what the exact value of said minimum consumption is. b) From the intervals of increase and decrease, justify why driving at $120\text{ km}/\text{h}$ consumes more than driving at $90\text{ km}/\text{h}$. Calculate the average rate of change $\text{TVM}[90, 120]$ and interpret its practical meaning by explaining how many extra liters the car consumes for each $\text{km}/\text{h}$ that exceeds the optimal speed in that section.

The following graph shows the monthly subscribers $S(t)$ (in thousands) of a digital magazine during its first year of operation ($t$ in months, from $t=0$ to $t=12$). Identify the intervals over which the number of subscribers increases and decreases. In which months are local maximums and minimums reached?

The attached graph does not represent a normal function $f(x)$, but rather the value of its Instantaneous Rate of Change (or rate of growth) at each point $x$. That is, if the graph shown is above the x-axis, the original function $f(x)$ is increasing; if it is below, it is decreasing. From this graph, deduce in which intervals the original function $f(x)$ is increasing and decreasing. At what exact value of $x$ will $f(x)$ reach a local extremum? Justify whether it is a maximum or a minimum.