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**Do Now – You Need a Calculator!!**

8.3 Trigonometry (Day 1) Understand what trigonometric ratios are and how to use them Do Now – You Need a Calculator!! Write the fraction as a decimal rounded to the nearest hundredth. 1. Solve each equation. 2. 0.29 x = 7.25 Success Criteria: Today’s Agenda Entry task Homework Check Lesson Notebook Check Happy Spring Break I can solve problems involving right triangles using trig ratios I can find sin, cos, tangent of an acute angle in a right triangle

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Do Not Copy – Listen!! By the AA Similarity Postulate, a right triangle with a given acute angle is similar to every other right triangle with that same acute angle measure. So ∆ABC ~ ∆DEF ~ ∆XYZ, and These are trigonometric ratios. A trigonometric ratio is a ratio of two sides of a right triangle.

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**It is pronounced "so - ka - toe - ah".**

SOH CAH TOA It is pronounced "so - ka - toe - ah". The SOH stands for "Sine of an angle is Opposite over Hypotenuse." The CAH stands for "Cosine of an angle is Adjacent over Hypotenuse." The TOA stands for "Tangent of an angle is Opposite over Adjacent." The Legend of SOH – CAH - TOA

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In trigonometry, the letter of the vertex of the angle is often used to represent the measure of that angle. For example, the sine of A is written as sin A. Writing Math

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Example 1 Write the trigonometric ratio as a fraction and as a decimal rounded to the nearest hundredth. sin B

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**Example 2: Finding Trigonometric Ratios**

Write the trigonometric ratio as a fraction and as a decimal rounded to the nearest hundredth. cos J

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**Example 3: Finding Trigonometric Ratios**

Write the trigonometric ratio as a fraction and as a decimal rounded to the nearest hundredth. tan K

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**Calculating Trigonometric Ratios**

Use your calculator to find the trigonometric ratio. Round to the nearest hundredth. sin 52° Be sure your calculator is in degree mode, not radian mode. Caution! sin 52° 0.79

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**Calculating Trigonometric Ratios**

Use your calculator to find the trigonometric ratio. Round to the nearest hundredth. cos 19° cos 19° 0.95

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**Example 4: Using Trigonometric Ratios to Find Lengths**

Find the length. Round to the nearest hundredth. is adjacent to the given angle, B. You are given AC, which is opposite B. Since the adjacent and opposite legs are involved, use a tangent ratio. BC Write a trigonometric ratio. Substitute the given values. Multiply both sides by BC and divide by tan 15°. BC ft Simplify the expression.

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Caution! Do not round until the final step of your answer. Use the values of the trigonometric ratios provided by your calculator.

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**Example 5: Using Trigonometric Ratios to Find Lengths**

Find the length. Round to the nearest hundredth. QR is opposite to the given angle, P. You are given PR, which is the hypotenuse. Since the opposite side and hypotenuse are involved, use a sine ratio. Write a trigonometric ratio. Substitute the given values. 12.9(sin 63°) = QR Multiply both sides by 12.9. 11.49 cm QR Simplify the expression.

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**No calculator draw the triangles**

8.3 Trigonometry Understand what trigonometric ratios are and how to use them Do Now: No calculator draw the triangles Use a special right triangle to write each trigonometric ratio as a fraction. 1. sin 60° cos 45° Success Criteria: Today’s Agenda I can solve problems involving right triangles using trig ratios I can find sin, cos, tangent of an acute angle in a right triangle

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**Example 1: Solving Right Triangles**

Find the unknown measures. Round angle measures to the nearest degree. Since the acute angles of a right triangle are complementary, mT 90° – 29° 61°.

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**Example 1: Discuss with your table:**

Now that you know the angle measures, how could you find the length of ST? Find the unknown measures. Round angle measures to the nearest degree. Since the acute angles of a right triangle are complementary, mT 90° – 29° 61°.

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If you know the sine, cosine, or tangent of an acute angle measure, you can use the inverse trigonometric functions to find the measure of the angle.

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**Example 2: Calculating Angle Measures from Trigonometric Ratios**

Use your calculator to find each angle measure to the nearest degree. A. cos-1(0.87) B. sin-1(0.85) C. tan-1(0.71) cos-1(0.87) 30° sin-1(0.85) 58° tan-1(0.71) 35°

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Example 2 Find the unknown measures. Round lengths to the nearest hundredth and angle measures to the nearest degree. Since the acute angles of a right triangle are complementary, mD = 90° – 58° = 32°. , so EF = 14 tan 32°. EF 8.75 DF2 = ED2 + EF2 DF2 = DF 16.51

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**Example 3: Identifying Angles from Trigonometric Ratios**

Use the trigonometric ratio to determine the measure of 1 and 2 .

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Example 4 Use the trigonometric ratio to determine the measure of 1 and 2 .

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Assignment #30 pg 510 #11-19, 22-24

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**8.3 Trigonometry Understand what trigonometric ratios are and how to use them**

Do Now: Use your calculator to find each trigonometric ratio. Round to the nearest hundredth. 1. tan 84° 2. cos 13° 9.51 0.97 Success Criteria: Today’s Agenda I can solve problems involving right triangles using trig ratios I can find sin, cos, tangent of an acute angle in a right triangle

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Lesson Quiz: Part II Find each length. Round to the nearest tenth. 5. CB 6. AC 6.1 16.2 Use your answers from Items 5 and 6 to write each trigonometric ratio as a fraction and as a decimal rounded to the nearest hundredth. 7. sin A cos A tan A

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**Example 2: Finding Trigonometric Ratios in Special Right Triangles**

Use a special right triangle to write cos 30° as a fraction. Draw and label a 30º-60º-90º ∆.

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**Use a special right triangle to write tan 45° as a fraction.**

Check It Out! Example 2 Use a special right triangle to write tan 45° as a fraction. s 45° Draw and label a 45º-45º-90º ∆.

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Do Now Find each length. Round to the nearest tenth. 1. CB 2. AC 6.1 16.2

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