SAT II Math II : Graphing Trigonometric Functions

Study concepts, example questions & explanations for SAT II Math II

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Example Questions

Example Question #1 : Graphing Trigonometric Functions

Give the amplitude of the graph of the function

\(\displaystyle f (x) = 2 \pi \sin 2 \pi x\)

Possible Answers:

\(\displaystyle 2 \pi\)

\(\displaystyle \pi\)

\(\displaystyle 2\)

\(\displaystyle 4 \pi\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 2 \pi\)

Explanation:

The amplitude of the graph of a sine function \(\displaystyle f(x) = A \sin Bx\) is \(\displaystyle A\). Here, \(\displaystyle A= 2 \pi\), so this is the amplitude.

Example Question #2 : Graphing Trigonometric Functions

Which of these functions has a graph with amplitude 4?

Possible Answers:

\(\displaystyle f(x) = 4 \cos \frac{\pi x}{5}\)

\(\displaystyle f(x) = \frac{1}{7}\cos \frac{\pi x }{4}\)

\(\displaystyle f(x) = \frac{1}{4}\cos \frac{\pi x}{3}\)

\(\displaystyle f(x) = 9\cos 4x\)

\(\displaystyle f(x) = \frac{2}{3}\cos \frac{ x }{4}\)

Correct answer:

\(\displaystyle f(x) = 4 \cos \frac{\pi x}{5}\)

Explanation:

The functions in each of the choices take the form of a cosine function 

\(\displaystyle f(x)= A \cos Nx\).

The graph of a cosine function in this form has amplitude \(\displaystyle A\). Therefore, for this function to have amplitude 4, \(\displaystyle A = 4\). Of the five choices, only 

\(\displaystyle f(x) = 4 \cos \frac{\pi x}{5}\)

matches this description.

Example Question #1 : Graphing Trigonometric Functions

Which of these functions has a graph with amplitude \(\displaystyle \frac{4}{7}\) ?

Possible Answers:

\(\displaystyle f(x)=\sin \frac{7x}{4}\)

\(\displaystyle f(x)=\sin \frac{4x}{7}\)

\(\displaystyle f(x)= \frac{4}{7} \sin x\)

\(\displaystyle f(x)=\sin \frac{4 \pi x}{7}\)

\(\displaystyle f(x)= \frac{2}{7} \sin x\)

Correct answer:

\(\displaystyle f(x)= \frac{4}{7} \sin x\)

Explanation:

The functions in each of the choices take the form of a sine function 

\(\displaystyle f(x)= A \sin Bx\).

The graph of a sine function in this form has amplitude \(\displaystyle A\). Therefore, for this function to have amplitude 4, \(\displaystyle A = \frac{4}{7}\). Of the five choices, only 

\(\displaystyle f(x)= \frac{4}{7} \sin x\)

matches this description.

Example Question #1 : Graphing Trigonometric Functions

Which of the following sine functions has a graph with period of 7?

Possible Answers:

\(\displaystyle f(x)= \frac{11}{5} \sin \frac{7 x}{2}\)

\(\displaystyle f(x)= \frac{11}{5} \sin \frac{2 x}{7}\)

\(\displaystyle f(x)= \frac{11}{5} \sin \frac{ \pi x}{7}\)

\(\displaystyle f(x)= \frac{11}{5} \sin \frac{7 \pi x}{2}\)

\(\displaystyle f(x)= \frac{11}{5} \sin \frac{2 \pi x}{7}\)

Correct answer:

\(\displaystyle f(x)= \frac{11}{5} \sin \frac{2 \pi x}{7}\)

Explanation:

The period of the graph of a sine function \(\displaystyle f(x)= A \sin B x\), is \(\displaystyle \frac{2 \pi}{B}\), or \(\displaystyle 2 \pi \div B\).

Therefore, we solve for \(\displaystyle B\):

\(\displaystyle \frac{2 \pi}{B} = 7\)

\(\displaystyle \frac{B}{2 \pi} = \frac{1}{7}\)

\(\displaystyle B= \frac{1}{7} \cdot 2 \pi = \frac{2 \pi}{7}\)

The correct choice is therefore \(\displaystyle f(x)= \frac{11}{5} \sin \frac{2 \pi x}{7}\).

Example Question #1 : Period And Amplitude

Which of the given functions has the greatest amplitude?

Possible Answers:

\(\displaystyle \sin(4x)\)

\(\displaystyle \sin(x+3)\)

\(\displaystyle \frac{1}{2}\sin(4x)\)

\(\displaystyle \sin\frac{2\pi }{3}(x+2)\)

\(\displaystyle 2\sin(x)\)

Correct answer:

\(\displaystyle 2\sin(x)\)

Explanation:

The amplitude of a function is the amount by which the graph of the function travels above and below its midline. When graphing a sine function, the value of the amplitude is equivalent to the value of the coefficient of the sine. Similarly, the coefficient associated with the x-value is related to the function's period. The largest coefficient associated with the sine in the provided functions is 2; therefore the correct answer is \(\displaystyle 2\sin(x)\).

The amplitude is dictated by the coefficient of the trigonometric function. In this case, all of the other functions have a coefficient of one or one-half.

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