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Common Core Standard  G.SRT.11  F.TF.3

How do you find the hypotenuse?

How do you label a triangle?

What is SOHCAHTOA?

How do you use SOHCAHTOA to find missing angles?

## Trig Functions are used with Right Triangles

Use the Pythagorean Theorem to find the length of the missing side.

12^2 +  x^2=13^2

144 + x^2 = 169

x^2 = 25  the square root of 25 =5 therefore x =5 which equals the opposite length

Now you have all three lengths

Opposite = 5

Hypotenuse = 13

Use  SOH CAH TOA  to remember the Trig functions

sin(θ) = Opposite/Hypotenuse 5/13

cos(θ) = Adjacent over hypotenuse 12/13.

tan(θ) = opposite over adjacent 5/12

# Memorize Trig functions using SOH CAH TOA

SOH CAH TOA has been used for years to help students remember the three most common trig ratios?  Trig ratios are used in geometry with right triangles to find missing angles or missing sides.  The three most common ratios are sin, cosine, and tangent. Let's look at some examples using SOHCAHTOA.

SOH helps one remember that sine equals Opposite over Hypotenuse

CAH helps one remember that cosine equals Adjacent over Hypotenuse

Cosine,Sine,and Tangent explained
 If you have the following information: A right angle Length of opposite leg Length of the hypotenuse Use Sin Opposite Hypotenuse

 A right angle Length of adjacent leg Length of the hypotenuse Use Cosine   Adjacent Hypotenuse

 A right angle Length of opposite leg Length of the adjacent Use Tangent   Opposite Adjacent

Missing Hypotenuse Length
Missing Opposite Length
Length of hypotenuse

## Find the missing length of a right triangle.

A six foot ladder leans against a building. If the ladder makes a 60∘ angle with the ground. How far up the wall does the ladder reach?

## Missing length of a right triangle word problem.

Step 1. Sketch the problem
Step 2.  Use SOH CAH TOA to remember the trig functions. In this problem you will use sine ( SOH = sin opposite hypotenuse )

Step. 3 Sin 60◦ = opposite / hypotenuse

Step 4. Sin 60∘ = x / 6

Step 5. Cross multiply

Step 6. 6 * sin 60∘ = 5.196 feet

Missing length of a triangle word problem 2.

A flagpole is 12 feet tall and perpendicular to the ground. A wire extends from the ground to the top of the pole. What is the angle of elevation from the bottom of the wire to the top of the flagpole?
Step 1. Create a drawing

Step 2. Using SOHCAHTOA you can determine you have Sin because you have opposite over hypotenuse

Step 3. In order to find an angle use inverse sin

Step 4. Take the inverse sin of 12 over 20 which equals 36.867

Step 5. Therefore, the angle of elevation is 36.867 degrees