Problem 39 - BIG IDEAS MATH Algebra 2: Common Core Student Edition 2015

Question

\(f(x)=5 \sec (x-\pi)\); translation 2 units down, followed by a reflection in the \(x\)-axis

Step-by-Step Solution

Answer

The transformed function is \(h(x) = -5\sec(x-\pi) + 2\)

Step 1: Apply the Vertical Translation

The vertical translation 2 units down means we subtract 2 from the original function: \(g(x) = f(x) - 2 = 5\sec(x-\pi) - 2\)

Step 2: Apply the Reflection in the x-axis

The reflection in the \(x\)-axis means we 'flip' the function by multiplying it by -1: \(h(x) = -g(x) = -(5\sec(x-\pi) - 2)\)

Step 3: Simplify The Final Function

Now, simplify the function to obtain the final transformed function: \(h(x) = -5\sec(x-\pi) + 2\)

Key Concepts

Vertical Translation

Vertical translation is a type of transformation that shifts a function up or down along the y-axis. This change is achieved by adding or subtracting a constant value to the function. For instance, in our exercise, the initial function is given by \(f(x) = 5 \sec(x - \pi)\). To perform a vertical translation, you subtract 2 from every point of the function. This is like taking the entire graph and moving it two units downward on the y-axis.

This operation is represented as:

• Original function: \(f(x)\)
• Translated function: \(g(x) = f(x) - 2\).

This results in the new equation \(g(x) = 5 \sec(x - \pi) - 2\). This simple shift affects all the y-values of your secant graph, lowering each by two units, without changing the x-values or the shape of the graph.

Reflection

Reflection is another powerful transformation that flips a graph over a line, often used to create a mirror image. In this context, a reflection in the x-axis means that every point \((x, y)\) on the graph becomes \((x, -y)\). This transformation is applied by multiplying the entire function by -1.

For our example, after the vertical translation, we have

• Function after vertical translation: \(g(x) = 5 \sec(x - \pi) - 2\).
• The reflection involves multiplying \(g(x)\) by -1.

Therefore, the reflected function \(h(x) = -g(x)\) becomes \(-5 \sec(x - \pi) + 2\).

This operation reverses all y-values of the function, effectively creating an upside-down graph. Any peak of the secant function turns into a trough and vice versa, while keeping the x-values unchanged.

Secant Function

The secant function, part of the family of trigonometric functions, is intimately linked with cosine. It is defined as \(\sec(x) = \frac{1}{\cos(x)}\).

This function exhibits interesting properties:

• It's undefined wherever the cosine is zero.
• It has vertical asymptotes, occurring at every odd multiple of \(\frac{\pi}{2}\) within its period.

The general form \(y = a \sec(bx - c) + d\) allows various transformations.

In the exercise, we start with \(f(x) = 5 \sec(x - \pi)\). Here:

• Amplitude: \(a = 5\), impacting the stretch vertically.
• Horizontal shift: \(-\pi\) translates the graph to the right by \(\pi\) units.

Through transformations—vertical translation and reflection—we derived \(h(x) = -5 \sec(x - \pi) + 2\), resulting in a final graph that is shifted vertically and reflected horizontally, showcasing how trigonometric transformations can drastically alter a function's appearance.