ACT Math : Cosine

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find The Period Of The Cosine

A function with period P will repeat on intervals of length P, and these intervals are referred to as periods.

 

Find the period of the function

.

Possible Answers:

Correct answer:

Explanation:

For the function

the period is equal to

or in this case

which reduces to .

Example Question #1 : How To Find The Period Of The Cosine

A function with period P will repeat on intervals of length P, and these intervals are referred to as periods.

 

Find the period of the function

.

Possible Answers:

Correct answer:

Explanation:

For the function

the period is equal to

or in this case

which reduces to .

Example Question #3 : How To Find The Period Of The Cosine

A function with period P will repeat on intervals of length P, and these intervals are referred to as periods.

 

Find the period of the function 

.

Possible Answers:

Correct answer:

Explanation:

For the function

the period is equal to

or in this case

which reduces to .

Example Question #4 : How To Find The Period Of The Cosine

A function with period  will repeat its solutions in intervals of length .

What is the period of the function ?

Possible Answers:

Correct answer:

Explanation:

For a trigonometric function , the period  is equal to . So, for .

Example Question #5 : How To Find The Period Of The Cosine

A function with period  will repeat its solutions in intervals of length .

What is the period of the function ?

Possible Answers:

Correct answer:

Explanation:

For a trigonometric function , the period  is equal to . So, for .

Example Question #6 : How To Find The Period Of The Cosine

A function with period  will repeat its solutions in intervals of length .

What is the period of the function ?

Possible Answers:

Correct answer:

Explanation:

For a trigonometric function , the period  is equal to . So, for .

Example Question #1 : How To Find The Range Of The Cosine

Simplify (cosΘ – sinΘ)2   

Possible Answers:

cos2Θ – 1

1 – sin2Θ

sin2Θ – 1

1 + sin2Θ

1 + cos2Θ

Correct answer:

1 – sin2Θ

Explanation:

Multiply out the quadratic equation to get cosΘ2 – 2cosΘsinΘ + sinΘ2  

Then use the following trig identities to simplify the expression:

sin2Θ = 2sinΘcosΘ

sinΘ2 + cosΘ2 = 1 

1 – sin2Θ is the correct answer for (cosΘ – sinΘ)2  

1 + sin2Θ is the correct answer for (cosΘ + sinΘ)2 

Example Question #2 : How To Find The Range Of The Cosine

Which of the following represents a cosine function with a range of  to ?

Possible Answers:

Correct answer:

Explanation:

The range of a cosine wave is altered by the coefficient placed in front of the base equation. So, if you have , this means that the highest point on the wave will be at  and the lowest at ; however, if you then begin to shift the equation vertically by adding values, as in, , then you need to account for said shift. This would make the minimum value to be  and the maximum value to be .

For our question, the range of values covers . This range is accomplished by having either  or  as your coefficient. ( merely flips the equation over the -axis. The range "spread" remains the same.) We need to make the upper value to be  instead of . To do this, you will need to subtract , or , from . This requires an downward shift of .  An example of performing a shift like this is:

Among the possible answers, the one that works is:

The  parameter does not matter, as it only alters the frequency of the function.

Example Question #3 : How To Find The Range Of The Cosine

Which of the following represents a cosine function with a range from  to ?

Possible Answers:

Correct answer:

Explanation:

The range of a cosine wave is altered by the coefficient placed in front of the base equation. So, if you have , this means that the highest point on the wave will be at  and the lowest at ; however, if you then begin to shift the equation vertically by adding values, as in, , then you need to account for said shift. This would make the minimum value to be  and the maximum value to be .  

For our question, the range of values covers . This range is accomplished by having either  or  as your coefficient. ( merely flips the equation over the -axis. The range "spread" remains the same.) We need to make the upper value to be  instead of . This requires an upward shift of . An example of performing a shift like this is:

Among the possible answers, the one that works is:

Example Question #4 : How To Find The Range Of The Cosine

What is the range of the trigonometric function defined by ?

Possible Answers:

Correct answer:

Explanation:

The range of a sine or cosine function spans from the negative amplitude to the positive amplitutde. The amplutide is given by  in the equation . Thus the range for our function is 

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