ACT Math : Trigonometry

Study concepts, example questions & explanations for ACT Math

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Example Questions

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

Which of the following statements is (are) true:

I. The domain of the tangent function is all real numbers

II. The range of the sine function is all real numbers

III. The periods of the tangent, sine, and cosine functions are the same.

Possible Answers:

II and III only

I and II only

II only

I only

none of the above

Correct answer:

II only

Explanation:

The domain of the tangent function does not include any values of x that are odd multiples of π/2 .

The range of the sine function is from [-1, 1].

The period of the tangent function is π, whereas the period for both sine and cosine is 2π.

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

Which of the following represents a sine wave with a range of ?

Possible Answers:

Correct answer:

Explanation:

The range of a sine 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, then, it is fine to use . The  for the function parameter only alters the period of the equation, making its waves "thinner."

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

Which of the following sine waves has a range of  to ?

Possible Answers:

Correct answer:

Explanation:

The range of a sine 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 add  to . This requires an upward 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 #1 : How To Find The Range Of The Sine

What is the range of the trigonometric function given by the equation:

Possible Answers:

Correct answer:

Explanation:

The range of the sine and cosine functions are the closed interval from the negative amplitude and the positive amplitude. The amplitude is given by the coefficient,  in the following general equation: 
. Thus we see the range is:

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

What is the range of the following trigonometric equation:
?

Possible Answers:

Correct answer:

Explanation:

The range of a sine or cosine function spans from the negative amplitude to the positive amplitude. The amplitude is  in the general formula: 
Thus we see amplitude of our function is  and so the range is:

Example Question #1 : How To Find Negative Sine

If , what is  if  is between  and ?

Possible Answers:

Correct answer:

Explanation:

Recall that .

Therefore, we are looking for  or .

Now, this has a reference angle of , but it is in the third quadrant. This means that the value will be negative. The value of  is . However, given the quadrant of our angle, it will be .

Example Question #2 : How To Find Negative Sine

What is the sine of the angle formed between the origin and the point  if that angle is formed with one side of the angle beginning on the -axis and then rotating counter-clockwise to ?

Possible Answers:

Correct answer:

Explanation:

You can begin by imagining a little triangle in the fourth quadrant to find your reference angle.  It would look like this:

Sin410

Now, to find the sine of that angle, you will need to find the hypotenuse of the triangle. Using the Pythagorean Theorem, , where  and  are leg lengths and  is the length of the hypotenuse, the hypotenuse is , or, for our data:

The sine of an angle is:

For our data, this is:

Since this is in the fourth quadrant, it is negative, because sine is negative in that quadrant.

Example Question #1 : How To Find Negative Sine

What is the sine of the angle formed between the origin and the point  if that angle is formed with one side of the angle beginning on the -axis and then rotating counter-clockwise to ?

Possible Answers:

Correct answer:

Explanation:

You can begin by imagining a little triangle in the third quadrant to find your reference angle. It would look like this: 

Sin38

Now, to find the sine of that angle, you will need to find the hypotenuse of the triangle. Using the Pythagorean Theorem, , where  and  are leg lengths and  is the length of the hypotenuse, the hypotenuse is , or, for our data:

The sine of an angle is:

For our data, this is:

Since this is in the third quadrant, it is negative, because sine is negative in that quadrant.

Example Question #61 : Trigonometry

If , what is the value of  if ?

Possible Answers:

Correct answer:

Explanation:

Recall that the  triangle appears as follows in radians:

454590rad

Now, the sine of  is . However, if you rationalize the denominator, you get:

Since , we know that  must be represent an angle in the third quadrant (where the sine function is negative). Adding its reference angle to , we get:

Therefore, we know that:

, meaning that 

Example Question #1 : How To Find Positive Sine

If , what is ?  Round to the nearest hundredth.

Possible Answers:

Correct answer:

Explanation:

Recall that the sine wave is symmetrical with respect to the origin. Therefore, for any value , the value for  is . Therefore, if  is , then for , it will be .

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