# Using the Tangent Function to Find the Angle (Mathematics Lesson)

# Using the Tangent Function to Find the Angle of a Right Triangle

The tangent function relates a given angle to the opposite side and adjacent side of a right triangle.The angle (labelled θ) is given by the formula below:

In this formula,

**θ**is an angle of a right triangle, the opposite is the length of the side opposite the angle and the adjacent is the length of side next to the angle. tan

^{-1}is the inverse tangent function (see

**Note**). The image below shows what we mean:

# How to Use the Tangent Function to Find the Angle of a Right Triangle

Finding the angle of a right triangle is easy when we know the opposite and the adjacent.#### An Example Question

What is the angle of the right triangle shown below?Step 1

θ = tan

^{-1}(opposite / adjacent)**Don't forget:**tan

^{-1}is the inverse tangent function (it applies to everything in the brackets)

**and**/ means ÷

Step 2

θ = tan

θ = tan

θ = tan

θ = 45°

The angle of a right triangle with an opposite of 5 cm and an adjacent of 5 cm is 45°.
^{-1}(5 / 5)θ = tan

^{-1}(5 ÷ 5)θ = tan

^{-1}(1)θ = 45°

# Remembering the Formula

Often, the hardest part of finding the unknown angle is remembering which formula to use.Whenever you have a right triangle where you know two sides and have to find an unknown angle...

......think trigonometry...

...............think sine, cosine or tangent...

........................think

**SOH CAH TOA**.

Looking at the example above, we know the

**O**pposite and the

**A**djacent.

The two letters we are looking for are

**OA**, which comes in the

**TOA**in SOH CAH

**TOA**.

This reminds us of the equation:

**T**an θ =

**O**pposite /

**A**djacent

^{-1}(see

**Note**).

θ =

**T**an^{-1}(**O**pposite /**A**djacent)# A Real Example of How to Use the Tangent Function to Find the Angle of a Right Triangle

The slider below gives another example of finding the angle of a right triangle (if the opposite and adjacent are known).##### Interactive Test

**show**

Here's a second test on finding the angle using the tangent function.

Here's a third test on finding the angle using the tangent function.

##### Note

# What Is the Inverse Tangent Function?

The inverse tangent function is the opposite of the tangent function.The tangent function takes in an angle, and gives the ratio of the opposite to the adjacent:

The inverse tangent function, tan

^{-1}, goes the other way. It takes the ratio of the opposite to the adjacent, and gives the angle:

# Switch Sides, Invert the Tangent

You may see the tangent function in an equation:To make theta the subject of the equation, take the inverse tangent of both sides.

The inverse tangent cancels out the tangent on the left hand side of the equals side, so the equation looks as below:

Comparing the two equations, the tangent has moved from one side of the equals sign to the other and has changed from

**tan**to

**tan**.

^{-1}(Note: the reverse is also true. A

**tan**can be moved to the other side of the equals sign, where it becomes a

^{-1}**tan**.)