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# introduction to trigonometric functions - PowerPoint PPT Presentation

Introduction to Trigonometric Functions. Return to home page. Trig functions are the relationships amongst various sides in right triangles. You know by the Pythagorean theorem that the sum of the squares of each of the smaller sides equals the square of the hypotenuse, .

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### You know in the above triangle that in right triangles.

Trig functions are how the relationships amongst the lengths of the sides of a right triangle vary as the other angles are changed.

How does this relate to trig? in right triangles.

• The opposite side divided by the hypotenuse, a/c, is called the sine of angle A

• The adjacent side divided by the hypotenuse, b/c, is called the cosine of Angle A

• The opposite side divided by the adjacent side, a/b, is called the tangent of Angle A

Remember SOHCAHTOA in right triangles.

• Sine is Opposite divided by Hypotenuse

• Cosine is Adjacent divided by Hypotenuse

• Tangent is Opposite divided by Adjacent

• SOHCAHTOA!!!!!!

• Examples

• Question 1

• Question 2

• Question 3

• Question 4

Example 1 in right triangles. If a = 3 and c = 6, what is the measurement of angle A?

Answer: a/c is a sine relationship with A. in right triangles. Sine A = 3/6 = .5, from your calculator, angle A = 30 degrees.

Example 2 in right triangles.

• A flagpole casts a 100 foot shadow at noon. Lying on the ground at the end of the shadow you measure an angle of 25 degrees to the top of the flagpole.

• How High is the flagpole?

How do you solve this question? in right triangles.

• You have an angle, 25 degrees, and the length of the side next to the angle, 100 feet. You are trying to find the length of the side opposite the angle.

• Opposite/adjacent is a tangent relationship

• Let x be the height of the flagpole

• From your calculator, the tangent of 25 is .47

• .47 =

• x = (.47)(100), x = 47

• The flagpole is 47 feet high.

Question 1 in right triangles.

• Given Angle A is 35 degrees, and b = 50 feet.

• Find c. Click on the correct answer.

• A. 61 feet

• B 87 feet

• C. 71 feet

GREAT JOB! in right triangles.

• You have an angle and an adjacent side, you need to find the hypotenuse. You knew that the cosine finds the relationship between the adjacent and the hypotenuse.

• Cosine 35 = 50/c, c Cosine 35 = 50,

• So c = 50/cos 35, or approximately 61

Next question

Nice try in right triangles.

• You have an angle and the adjacent side. You want to find the hypotenuse.

• What relationship uses the adjacent and the hypotenuse?

Back to

Question

Back to tutorial

Question 2 in right triangles.

• If the adjacent side is 50, and the hypotenuse is 100, what is the angle? Please click on the correct answer.

• A. 60 degrees

• B. 30 degrees

• C. 26 degrees

Way to go! in right triangles.

• Given the adjacent side and the hypotenuse, you recognized that the adjacent divided by the hypotenuse was a cosine relationship.

• Cosine A = 50/100,

• A = 60 degrees

Next question

Nice try in right triangles.

• Given an adjacent side and a hypotenuse, what relationship will give you the angle?

Back to question

Back to tutorial

Question 3 in right triangles.

• If the opposite side is 75, and the angle is 80 degrees, how long is the adjacent side?

• A. 431

• B. 76

• C. 13

Nice job in right triangles.

• You were given the opposite side of 75 and an angle of 80 degrees and were asked to find the adjacent side. You recognized that this was a tangent relationship.

• Tangent 80 = 75/b,

• b tangent 80 = 75,

• b = = 13

Next question

Nice Try in right triangles.

• You are given an angle and the opposite side, and have been asked to find the adjacent side. What relationship uses the opposite side and the adjacent side?

Back to question

Back to tutorial

Question 4: in right triangles. If B = 50 degrees and b = 100 what is c?

B

A. 155

c

________

B. 130

___________

a

________

A

C

C. 84

b

Nice try in right triangles.

• What is the relationship between B and b? And, what is the relationship between b and c?

Great job! in right triangles.

• First, you recognized that b is the opposite side from B. Then, you recognized that the relationship between an opposite side and the hypotenuse is a sine relationship.

• Sine 50 = 100/c, c Sine 50 = 100, c = 100/sine 50 = 130.

Go to next section

Introduction to Quadrants in right triangles.

90 degrees

II

I

180 degrees______________________ 0 degrees

__________________

IV

III

270 degrees

• All angles are divided into 4 quadrants

• Angles between 0 and 90 degrees are in quadrant 1

• Angles between 90 and 180 degrees are in quadrant II

• Angles between 180 and 270 degrees are in quadrant III

• Angles between 270 and 360 degrees are in quadrant IV

• Why is this important? Click and find out!

Importance of quadrants in right triangles.

• Different trig functions are positive and negative in different quadrants.

• The easy way to remember which are positive and negative in each quadrant it to remember, “All Students Take Classes”

All Students Take Classes in right triangles.

• Quadrant I: 0 – 90 degrees: All: All trig functions are positive

• Quadrant II: 90 – 180 degrees: Students: Sine functions are positive

• Quadrant III: 180 – 270 degrees: Take: Tangent functions are positive

• Quadrant IV: 270 – 360 degrees: Classes; Cosine functions are positive

Standard Angle Values in right triangles.

Remember in right triangles.

• Simplify the fractions

• Place the radicals in the numerator. Write