Trigonometry
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ACT Math › Trigonometry
Find the domain of . Assume 
 is for all real numbers.
Explanation
The domain of  does not exist at 
, for 
 is an integer.
The ends of every period approaches to either positive or negative infinity. Notice that for this problem, the entire graph shifts to the right  units. This means that the asymptotes would also shift right by the same distance.
The asymptotes will exist at:
Therefore, the domain of  will exist anywhere EXCEPT:
If  and 
, what is the value of 
?
Explanation
Based on this data, we can make a little triangle that looks like:

This is because .
Now, this means that  must equal 
. (Recall that the cosine function is negative in the second quadrant.) Now, we are looking for:
 or 
. This is the cosine of a reference angle of:
Looking at our little triangle above, we can see that the cosine of  is 
.
If  and 
, what is the value of 
?
Explanation
Based on this data, we can make a little triangle that looks like:

This is because .
Now, this means that  must equal 
. (Recall that the cosine function is negative in the second quadrant.) Now, we are looking for:
 or 
. This is the cosine of a reference angle of:
Looking at our little triangle above, we can see that the cosine of  is 
.
A sine function has a period of , a 
-intercept of 
, an amplitude of 
 and no phase shift. These describe which of these equations?
Explanation
Looking at this form of a sine function:
We can draw the following conclusions:
- because the amplitude is specified as - . 
- because of the specified period of - since - . 
- because the problem specifies there is no phase shift. 
- because the - -intercept of a sine function with no phase shift is - . 
Bearing these in mind,  is the only function that fits all four of those.
Using trig identities, simplify sinθ + cotθcosθ
tanθ
secθ
sin2θ
cos2θ
cscθ
Explanation
Cotθ can be written as cosθ/sinθ, which results in sinθ + cos2θ/sinθ.
Combining to get a single fraction results in (sin2θ + cos2θ)/sinθ.
Knowing that sin2θ + cos2θ = 1, we get 1/sinθ, which can be written as cscθ.
Given a function , what is a valid domain?
Explanation
The function  is related to the parent function 
.
The domain of the parent function is . The values 
 and 
 will not affect the domain of the curve.
The answer is .
What is the domain of the function  ?
Explanation
The domain of a function refers to all possible values of  for which an answer can be obtained. Cosine, as a function, cycles endlessly between 
 and 
 (subject to modifiers of the amplitude). Because there is no real number value that can be inserted into 
 in this case which does not produce a value between 
 and 
, the domain of cosine is effectively infinite.
What is the period of the function ?
Explanation
To find the period of Sine and Cosine functions you use the formula:
 where 
 comes from 
. Looking at our formula you see b is 4 so
A man has a rope that is  long, attached to the top of a small building. He pegs the rope into the ground at an angle of 
. How far away from the building did he walk horizontally to attach the rope to the ground? Round to the nearest inch.
Explanation
Begin by drawing out this scenario using a little right triangle:

We know that the cosine of an angle is equal to the ratio of the side adjacent to that angle to the hypotenuse of the triangle. Thus, for our triangle, we know:
Using your calculator, solve for :
This is . Now, take the decimal portion in order to find the number of inches involved.
Thus, rounded, your answer is  feet and 
 inches.
A man has a rope that is  long, attached to the top of a small building. He pegs the rope into the ground at an angle of 
. How far away from the building did he walk horizontally to attach the rope to the ground? Round to the nearest inch.
Explanation
Begin by drawing out this scenario using a little right triangle:

We know that the cosine of an angle is equal to the ratio of the side adjacent to that angle to the hypotenuse of the triangle. Thus, for our triangle, we know:
Using your calculator, solve for :
This is . Now, take the decimal portion in order to find the number of inches involved.
Thus, rounded, your answer is  feet and 
 inches.