Precalculus : Find the Amplitude of a Sine or Cosine Function

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Find The Amplitude Of A Sine Or Cosine Function

What is the amplitude of \(\displaystyle y=3\sin\left(\frac{x}{5}\right)}\)?

Possible Answers:

\(\displaystyle 5\)

\(\displaystyle \frac{1}{5}\)

\(\displaystyle 3\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 3\)

Explanation:

For any equation in the form \(\displaystyle y=a\sin(bx)\), the amplitude of the function is equal to \(\displaystyle \left | a\right |\).

In this case, \(\displaystyle a=3\) and \(\displaystyle b=\frac{1}{5}\), so our amplitude is \(\displaystyle 3\).

Example Question #51 : Graphing The Sine And Cosine Functions

What is the amplitude of \(\displaystyle F(t)=5sin(2x-1)\)?

Possible Answers:

\(\displaystyle -1\)

\(\displaystyle 8\)

\(\displaystyle 5\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 5\)

Explanation:

The formula for the amplitude of a sine function is \(\displaystyle A\) from the form:

 \(\displaystyle F(t)=Asin(Bt-C)+D\).

In our function, \(\displaystyle A=5\).

Therefore, the amplitude for this function is \(\displaystyle 5\).

Example Question #1 : Find The Amplitude Of A Sine Or Cosine Function

Find the amplitude of the following trig function:  \(\displaystyle y=-2-3sin(2\theta-5)\)

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle -2\)

\(\displaystyle 2\)

\(\displaystyle \frac{3}{2}\)

\(\displaystyle -3\)

Correct answer:

\(\displaystyle 3\)

Explanation:

Rewrite \(\displaystyle y=-2-3sin(2\theta-5)\) so that it is in the form of:

\(\displaystyle y=Asin(Bx+C)+D\)

\(\displaystyle y=-3sin(2\theta-5)-2\)

The absolute value of \(\displaystyle A\) is the value of the amplitude.

\(\displaystyle \textup{Amplitude= }\left | A\right |= \left | -3\right |=3\)

Example Question #4 : Find The Amplitude Of A Sine Or Cosine Function

Find the amplitude of the function.

\(\displaystyle y=5sin\, x\)

Possible Answers:

\(\displaystyle 5\)

\(\displaystyle 1\)

\(\displaystyle 10\)

\(\displaystyle x\)

Correct answer:

\(\displaystyle 5\)

Explanation:

For the sine function

\(\displaystyle y=Asin\, x\) where \(\displaystyle A\epsilon \, \mathbb{R}\)

the amplitude is given as \(\displaystyle \left | A\right |\) .

As such the amplitude for the given function

\(\displaystyle y=5sin\, x\) is

\(\displaystyle \left | 5\right |=5\).

Example Question #1 : Trigonometric Graphs

Which of the given functions has the greatest amplitude?

Possible Answers:

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

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

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

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

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

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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