# What Are The Output Values Of Cosine? (5 Key Values To Know)

In trigonometry, you will sometimes see common input angles (such as 45 or 90 degrees) for the cosine function.  It helps to know the corresponding outputs for these angles to help you do calculations faster.

So, what are the output values of cosine?  Five output values of cosine you should know are cos(0) = 1, cos(π/6) = √3/2, cos(π/4) = √2/2, cos(π/3) = 1/2, and cos(π/2) = 0 These output values correspond to the common degree measures 0o, 30o, 45o, 60o, and 90o. Using the negative of these angles as input gives us the same outputs.

Of course, when the input angle for cosine is in quadrants 2 or 3 (angles between 90o and 270o, or π/2 to 3π/2 radians), we get negative values for cosine.  When the input angle for cosine is in quadrants 1 or 4 (angles between 0o and 90o or 270o and 360o), we get positive values for cosine.

In this article, we’ll talk about some output values for cosine and how to remember the 5 common ones we listed above.  We’ll also review the signs of the outputs for cosine and when they are positive, negative, or zero.

Let’s get started.

## What Are The Output Values Of Cosine?

The output values of cosine are given in the table below for 5 common values:

As an easy way to remember the values, note that each output value has the form √n/2, where n goes from 4 to 0 as we move from the degree measures 0 to 90o (0 to π/2 radians):

• For 0o: use n = 4, so the output is sin(0o) = √4/2 = 2/2 = 1.
• For 30o: use n = 3, so the output is sin(30o) = √3/2.
• For 45o: use n = 2, so the output is sin(45o) = √2/2.
• For 60o: use n = 1, so the output is sin(60o) = √1/2 = 1/2.
• For 90o: use n = 0, so the output is sin(90o) = √0/2 = 0/2 = 0.

Remember that we measure reference angles from the x-axis to get an acute angle (less than 90 degrees).  This means that in the 2nd quadrant, we subtract the angle from 180 degrees (π radians) to get our reference angle.

Also, keep in mind that the output values of cosine are negative in the 2nd quadrant.

So, in the 2nd quadrant, we would get the following reference angles and output values for cosine:

In the 3rd quadrant, we subtract 180 degrees (π radians) from the angle to get our reference angle.

So, in the 3rd quadrant, we would get the following reference angles and output values for cosine:

In the 4th quadrant, we subtract the angle from 360 degrees (2π radians) to get our reference angle.

Also, the output values of cosine are positive in the 4th quadrant.

In the 4th quadrant, we would get the following reference angles and output values for cosine:

Finally, remember that for a negative angle, we add 360 degrees (2π radians) until we get to an angle between 0o and 360o.

For an angle greater than 360o, we do the opposite and subtract 360 degrees (2π radians) until we get to an angle between 0o and 360o.

### Examples Of Output Values Of Cosine

Let’s take a look at some examples to show how to find the output values of cosine for various input angles.

#### Example 1: Cosine In The First Quadrant

Let’s say that we have the angle A = 60o, which is in the first quadrant (it is between 0o and 90o).

To find the cosine of the angle A, all we need to do is look up the value in the first table above.

So:

• cos(A)
• =cos(60o)
• =1/2

#### Example 2: Cosine In The Second Quadrant

Let’s say that we have the angle A = 150o, which is in the second quadrant (it is between 90o and 180o).

To find the cosine of the angle A, we will first need to find the reference angle A’.  In the second quadrant, we calculate

• A’ = 180o – A
• A’ = 180o – 150o
• A’ = 30o

Also, we know that cosine has negative output in the 2nd quadrant.  Now, we need to look up the value in the first table above.

So:

• cos(A)
• =cos(150o)
• =-cos(30o)  [using our reference angle, A’ = 30o, and cosine is negative in the 2nd quadrant]
• =-√3/2  [cos(30o) = √3/2, from the table above]

#### Example 3: Cosine In The Third Quadrant

Let’s say that we have the angle A = 225o, which is in the third quadrant (it is between 180o and 270o).

To find the cosine of the angle A, we will first need to find the reference angle A’.  In the third quadrant, we calculate

• A’ = A – 180o
• A’ = 225o – 180o
• A’ = 45o

Also, we know that cosine has negative output in the 3rd quadrant.  Now, we need to look up the value in the first table above.

So:

• cos(A)
• =cos(225o)
• =-cos(45o)  [using our reference angle, A’ = 45o, and cosine is negative in the 3rd quadrant]
• =-√2/2  [cos(45o) = √2/2, from the table above]

#### Example 4: Cosine In The Fourth Quadrant

Let’s say that we have the angle A = 330o, which is in the fourth quadrant (it is between 270o and 360o).

To find the cosine of the angle A, we will first need to find the reference angle A’.  In the fourth quadrant, we calculate

• A’ = 180o – A
• A’ = 360o – 330o
• A’ = 30o

Also, we know that cosine has positive output in the 4th quadrant.  Now, we need to look up the value in the first table above.

So:

• cos(A)
• =cos(330o)
• =cos(30o)  [using our reference angle, A’ = 30o, and cosine is positive in the 4th quadrant]
• =√3/2  [cos(30o) = √3/2, from the table above]

#### Example 5: Cosine Of A Negative Angle

Let’s say that we have the angle A = -150o, which is negative.  So, we will add 360o until we get an angle measure between 0o and 360o.

This gives us B = -150o + 360o = 210o.

To find the cosine of the angle A = -150o, we can find the cosine of angle B = 210o (note that B = 210o is in the 3rd quadrant, since it is between 180o and 270o).

First, we need to find the reference angle B’.  In the 3rd quadrant, we calculate

• B’ = B – 180o
• B’ = 210o – 180o
• B’ = 30o

Also, we know that cosine has negative output in the 3rd quadrant.  Now, we need to look up the value in the first table above.

So:

• cos(A)
• =cos(B)
• =cos(210o)
• =-cos(30o)  [using our reference angle, B’ = 30o, and cosine is negative in the 3rd quadrant]
• =-√3/2  [cos(30o) = √3/2, from the table above]

#### Example 6: Cosine Of An Angle Greater Than 360o

Let’s say that we have the angle A = 630o, which is greater than 360o.  So, we will subtract 360o until we get an angle measure between 0o and 360o.

This gives us B = 630o – 360o = 270o.

To find the cosine of the angle A = 630o, we can find the cosine of angle B = 270o (note that B = 270o is on the border between the 3rd and 4th quadrants, since 270o is the cutoff).

First, we need to find the reference angle B’.  We calculate

• B’ = B – 180o
• B’ = 270o – 180o
• B’ = 90o

Also, we know that cosine has negative output in the 3rd quadrant.  Now, we need to look up the value in the first table above.

So:

• cos(A)
• =cos(B)
• =cos(270o)
• =-cos(90o)  [using our reference angle, B’ = 90o, and cosine is negative in the 3rd quadrant]
• =0  [cos(90o) = 0, from the table above]

## Conclusion

Now you know more about the output values of cosine and how they change as input angles change.  You also know how to figure out the sign of the outputs, based on the quadrant of the input angle.