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\(f(x)=\sin x\) (a) What is the \(y\) -intercept of the graph of \(f ?\) (b) For what numbers \(x,-\pi \leq x \leq \pi,\) is the graph of \(f\) increasing? (c) What is the absolute maximum of \(f ?\) (d) For what numbers \(x, 0 \leq x \leq 2 \pi, \operatorname{does} f(x)=0 ?\) (e) For what numbers \(x,-2 \pi \leq x \leq 2 \pi,\) does \(f(x)=1 ?\) Where does \(f(x)=-1 ?\) (f) For what numbers \(x,-2 \pi \leq x \leq 2 \pi,\) does \(f(x)=-\frac{1}{2} ?\) (g) What are the \(x\) -intercepts of \(f ?\)

Short Answer

Expert verified
a) 0. b) \( -\pi/2 < x < \pi/2 \). c) 1. d) 0, \( \pi \), \( 2\pi \). e) \( \pi/2 \), \( 5\pi/2 \); \( -3\pi/2 \), \( 3\pi/2 \). f) \( -7\pi/6 \), \( -5\pi/6 \), \( 5\pi/6 \), \( 7\pi/6 \). g) \( k\pi \).

Step by step solution

01

Find the y-intercept

The y-intercept of a function is the value of the function when x = 0. For the function \( f(x) = \sin x \), we find \( f(0) \). Since \( \sin 0 = 0 \), the y-intercept is 0.
02

Determine where the graph is increasing

To determine where \( f(x) = \sin x \) is increasing within the interval \( -\pi \leq x \leq \pi \), find where the derivative \( f'(x) = \cos x \) is positive. \(\cos x \) is positive when \( -\pi/2 < x < \pi/2 \). So, the graph is increasing on the interval \( -\pi/2 < x < \pi/2 \).
03

Find the absolute maximum

The absolute maximum of \( \sin x \) is 1, which occurs at \( x = \pi/2 \).
04

Find where \( f(x) = 0 \) in \( 0 \leq x \leq 2\pi \)

Solve \( \sin x = 0 \) for \( 0 \leq x \leq 2\pi \). \( \sin x = 0 \) at \( x = 0, \pi, \text{and } 2\pi \).
05

Find where \( f(x) = 1 \) and where \( f(x) = -1 \)

Solve \( \sin x = 1 \) for \( -2\pi \leq x \leq 2\pi \). \( \sin x = 1 \) at \( x = \pi/2 \) and \( x = 5\pi/2 \). Solve \( \sin x = -1 \) for \( -2\pi \leq x \leq 2\pi \). \( \sin x = -1 \) at \( x = -3\pi/2 \) and \( x = 3\pi/2 \).
06

Find where \( f(x) = -1/2 \)

Solve \( \sin x = -1/2 \) for \( -2\pi \leq x \leq 2\pi \). \( \sin x = -1/2 \) at \( x = -7\pi/6, -5\pi/6, 5\pi/6, \text{ and } 7\pi/6 \).
07

Find the x-intercepts

The x-intercepts are the values of x where \( f(x) = 0 \), which are found by setting \( \sin x = 0 \). Thus, the x-intercepts occur at \( x = k\pi \), where k is any integer.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Y-Intercept
The y-intercept of a function is the point where the graph intersects the y-axis. This happens when the input value, x, is zero. For the sine function, expressed as \(f(x) = \sin x\), we need to find \(f(0)\). Since \(\sin 0 = 0\), the y-intercept is 0.

In other words, the point (0,0) is where the graph of \(f(x) = \sin x\) crosses the y-axis.

Remember, the y-intercept gives us a helpful starting point to begin plotting the function graph.
Increasing Intervals
A function is said to be increasing on an interval if as x increases, f(x) also increases. To determine where \(f(x) = \sin x\) is increasing, we look at the derivative \(f'(x) = \cos x\).

The sine function increases where its derivative, cosine, is positive. Cosine is positive in the interval \(-\pi/2 < x < \pi/2\). This means that the sine function is increasing on this interval within the given range \(-\pi \leq x \leq \pi\).

Therefore, the graph of \(f(x) = \sin x\) is increasing between \(-\pi/2\) and \(\pi/2\), which translates to the interval \(-1.57 < x < 1.57\) in radians.
Absolute Maximum
The absolute maximum of a function is the highest point over its entire domain. For the function \(f(x) = \sin x\), the absolute maximum value is 1. This occurs at specific points where sine reaches its peak.

Specifically, within one cycle of the sine function (from \(-\pi\) to \(\pi\)), the absolute maximum of 1 occurs at \(x = \pi/2\).

It's important to note that sine function is periodic, so this maximum value of 1 repeats at intervals \(2n\pi + \pi/2\) where n is any integer.
Zeros of Function
The zeros of a function are the values of x at which \(f(x) = 0\). For the sine function, these are the points where the sine curve crosses the x-axis.

Solve \(\sin x = 0\) within the interval \(0 \leq x \leq 2\pi\). The function equals zero at \(x = 0, \pi, \) and \(2\pi\).

These points, (0, 0), (\pi, 0), and (2\pi, 0), represent the x-values where the function touches the x-axis without going above or below it.
X-Intercepts
X-intercepts are similar to zeros. They are the points where the graph of the function crosses the x-axis. For \(f(x) = \sin x\), the x-intercepts occur where the function equals zero.

We know that \(\sin x = 0\) at integer multiples of \(\pi\). Therefore, the x-intercepts for \(\sin x\) are at points \(x = k\pi\), where k is any integer.

For instance, within the range \(-2\pi \leq x \leq 2\pi\), the x-intercepts are at \(-2\pi, -\pi, 0, \pi, \text{and } 2\pi\). These points summarize where the sine wave meets the x-axis.

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