# Sin Cos Tan

Here you will learn about sin cos tan (sine, cosine, tangent), including understanding what these three trigonometric functions are and their ratios, when to use these functions, their inverses, and how to use them.

Students will first learn about sin cos tan as part of geometry in high school.

## What is sin cos tan?

Sin cos tan is a shortened description of the three trigonometric functions of sine, cosine, and tangent. These functions associate the ratio of two sides of a right-angled triangle with an angle.

To calculate using sin, cos and tan, you need to know their trigonometric ratios (remember that the ratio of two values is a division of these values).

Consider the right-angled triangle below.

• \theta is the angle
• The opposite side \textbf{(O)} to the angle
• The adjacent side \textbf{(A)} (next to) the angle
• The hypotenuse \textbf{(H)} the longest side (always the side facing the right-angle)

The three trigonometric ratios can be used to determine a missing side or a missing angle. You use the following trigonometric formulae.

If you look at the letters only within the three triangles above, you get the abbreviation SOHCAHTOA where:

\quad - \quad \textbf{SOH} is the association of the sine of an angle (S) with the opposite side \hspace{0.85cm} (O) and the hypotenuse (H), of the triangle.

\quad - \quad \textbf{CAH} is the association of the cosine of an angle (C) with the adjacent side \hspace{0.85cm} (A) and the hypotenuse (H) of the triangle.

\quad - \quad \textbf{TOA} is the association of the tangent of an angle (T) with the opposite side \hspace{0.85cm} (O) and the adjacent side (A) of the triangle.

Step-by-step guide: SOHCAHTOA

You use one of the three trigonometric ratios of \textbf{sin} \, \bf{\theta}, \, \textbf{cos} \, \bf{\theta}, and \textbf{tan} \, \bf{\theta} to find one of the missing sides of a right angled triangle when you know another angle, apart from the right-angle.

You use the inverse functions of the three trigonometric ratios to determine a missing angle \theta (Greek letter theta).

• The inverse sine function is written as \theta=\sin^{-1}\left(\cfrac{O}{H}\right).
• The inverse cosine function is written as =\theta=\cos^{-1}\left(\cfrac{A}{H}\right).
• The inverse tangent function is written as \theta=\tan^{-1}\left(\cfrac{O}{A}\right).

Step-by-step guide: Trigonometric functions

## Common Core State Standards

How does this relate to high school math?

• High School – Geometry – Similarity, Right Triangles, & Trigonometry (HS.G.SRT.C.6)
Understand that by similarity, side ratios in right triangles are properties of the angles in the triangle, leading to definitions of trigonometric ratios for acute angles.

• High School – Geometry – Similarity, Right Triangles, & Trigonometry (HS.G.SRT.C.8)
Use trigonometric ratios and the Pythagorean Theorem to solve right triangles in applied problems.

## How to calculate using sin cos tan

In order to calculate using sin cos tan:

1. Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.
2. Choose the trig ratio you need.
3. Substitute the values from the triangle into the function.
4. Calculate the unknown side or angle, rearranging if necessary.

## Sin cos tan examples

### Example 1: missing side (sine)

Determine the length of the hypotenuse for the triangle ABC below.

1. Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.

Labeling the sides in relation to the angle, you have,

2Choose the trig ratio you need.

You know that \theta=42^{\circ}, \, O=7 and H=x. Using SOHCAHTOA, you can use the sine ratio (SOH) to determine the missing length of the hypotenuse.

3Substitute the values from the triangle into the function.

Substituting these values into the trigonometry formula \sin \theta=\cfrac{O}{H}, you have \sin{42}=\cfrac{7}{x}.

4Calculate the unknown side or angle, rearranging if necessary.

You need x to be the subject of the formula and so you first have to multiply both sides by x to get,

x\times\sin{42}=7

Dividing both sides of the equation by \sin{42}, you get

x=\cfrac{7}{\sin{42}}=10.46133585…

The length of the hypotenuse x=10.46 \; cm\text{ (nearest hundredth)}.

### Example 2: missing side (cosine)

Determine the length of the adjacent side for the triangle PQR below.

Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.

Choose the trig ratio you need.

Substitute the values from the triangle into the function.

Calculate the unknown side or angle, rearranging if necessary.

### Example 3: missing side (tangent)

Determine the length of the adjacent side for the triangle EFG below.

Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.

Choose the trig ratio you need.

Substitute the values from the triangle into the function.

Calculate the unknown side or angle, rearranging if necessary.

### Example 4: missing angle (sine)

Determine the size of the angle \theta for the triangle ABC below.

Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.

Choose the trig ratio you need.

Substitute the values from the triangle into the function.

Calculate the unknown side or angle, rearranging if necessary.

### Example 5: missing side (cosine)

Determine the size of the angle \theta for the triangle STU below.

Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.

Choose the trig ratio you need.

Substitute the values from the triangle into the function.

Calculate the unknown side or angle, rearranging if necessary.

### Example 6: missing side (tangent)

Determine the size of the angle \theta for the triangle XYZ below.

Label the sides of the right-angled triangle that you have information about in relation to the angle \bf{\theta}.

Choose the trig ratio you need.

Substitute the values from the triangle into the function.

Calculate the unknown side or angle, rearranging if necessary.

### Teaching tips for sin cos tan

• Introduce the unit circle to explain how these functions work for all angles, not just those in right triangles.

• Use real-world scenarios, such as calculating heights of objects using angles of elevation or depression, to illustrate the practical use of trigonometry.

• Introduce basic trigonometric identities, such as \sin^{2}\theta + \cos^{2}\theta=1, to deepen understanding and provide tools for simplifying expressions.

### Easy mistakes to make

• Thinking a right-angled triangle is different from a right triangle
Right-angled triangles are sometimes called right triangles.

• Not knowing when to use SOHCAHTOA
You can use SOHCAHTOA to find a missing side of a right-angled triangle when you have another side and a given angle.

You can use SOHCAHTOA to find a missing angle of a right-angled triangle when you have two given side lengths.

If you have two sides and you want to find the third side of the triangle, you can use the Pythagorean theorem a^{2}+b^{2}=c^{2}.

• Not knowing when to use standard or inverse trig function
You use standard trig functions when you know the angle. You have to use the inverse trig functions when you don’t know the angle.

### Practice sin cos tan questions

1. Determine the length of the missing side of the right triangle below. Write your answer correct to the nearest hundredth ( 2 decimal places).

4.67 \, cm

6.02 \, cm

12.11 \, cm

13.45 \, cm

From the angle \theta=42^{\circ} you know that O=9 and H=x so you use the sine ratio, \sin\theta=\cfrac{O}{H}.

\sin{42}=\cfrac{9}{x}

x=\cfrac{9}{\sin{42}}=13.45028895…=13.45 \, cm\text{ (nearest hundredth)}

2. Determine the length of the missing side of the right triangle below. Write your answer correct to the nearest hundredth.

20.90 \, cm

23.37 \, cm

64.18 \, cm

67.8 \, cm

From the angle \theta=19^{\circ} you know that A=22.1 and H=x so you use the cosine ratio, \cos\theta=\cfrac{A}{H}.

\cos{19}=\cfrac{22.1}{x}

x=\cfrac{22.1}{\cos{19}}=23.37341705…=23.37 \, cm\text{ (nearest hundredth)}

3. Determine the length of the missing side of the right triangle below. Write your answer correct to the nearest tenth.

28.8 \, cm

0.1 \, cm

7.7 \, cm

1.2 \, cm

From the angle \theta=72^{\circ} you know that O=x and A=0.4 so you use the tangent ratio, \tan\theta=\cfrac{O}{A}.

\tan{72}=\cfrac{x}{0.4}

x=0.4\times\tan{72}=1.231073415…=1.2 \, cm\text{ (nearest tenth)}

4. Determine the length of the missing angle \theta in the right triangle below.

26.57^{\circ}\text{ (nearest hundredth)}

30^{\circ}

60^{\circ}

63.43^{\circ}\text{ (nearest hundredth)}

From the angle \theta you know that O=2.2 and H=4.4. As you need to find the angle, you use the inverse sine ratio, \theta=\sin^{-1}\left(\cfrac{O}{H}\right).

\theta=\sin^{-1}\left(\cfrac{2.2}{4.4}\right)=30^{\circ}

5. Determine the length of the missing angle \theta in the right triangle below. Write your answer to the nearest tenth.

80.4^{\circ}

9.4^{\circ}

9.6^{\circ}

48.4^{\circ}

From the angle \theta you know that A=1.03 and H=6.2. As you need to find the angle, you use the inverse cosine ratio, \theta=\cos^{-1}\left(\cfrac{A}{H}\right).

\theta=\cos^{-1}\left(\cfrac{1.03}{6.2}\right)=80.4^{\circ} \text{ (nearest hundredth)}

6. Determine the length of the missing angle \theta in the right triangle below. Write your answer to the nearest hundredth.

43.18^{\circ}

20.21^{\circ}

69.79^{\circ}

46.82^{\circ}

From the angle \theta you know that O=6.5 and A=6.1. As you need to find the angle, you use the inverse tangent ratio, \theta=\tan^{-1}\left(\cfrac{O}{A}\right).

\theta=\tan^{-1}\left(\cfrac{6.5}{6.1}\right)=46.81830296…=46.82^{\circ}\text{ (nearest hundredth)}

## Sin Cos Tan FAQs

What is a mnemonic device for sin cos tan?

A common mnemonic device for remembering the trigonometric functions sine, cosine, and tangent is: SOH CAH TOA.
Sine = Opposite/Hypotenuse

How do you use a calculator to find sin, cos, and tan?

Most calculators have dedicated sin, cos, and tan buttons. To find the value of these functions for a specific angle, input the angle and press the corresponding button. Make sure the calculator is set to the correct mode (degrees or radians) depending on the angle’s unit.

What is the unit circle, and how is it related to sin, cos, and tan?

The unit circle is a circle with a radius of 1 centered at the origin of the coordinate plane. The coordinates of a point on the unit circle correspond to the cosine and sine of the angle formed by the radius and the positive x -axis. The tangent of an angle can be found by dividing the value of sin by the value of cos.

What are the reciprocal functions of sin, cos, and tan?

Cosecant (csc) is the reciprocal of sine: csc(\theta) = \frac{1}{\sin(\theta)}

Secant (sec) is the reciprocal of cosine: sec(\theta) = \frac{1}{\cos(\theta)}

Cotangent (cot) is the reciprocal of tangent: cot(\theta) = \frac{1}{\tan(\theta)}

## The next lessons are

• Circle math
• Sectors arcs and segments
• Circle theorems

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