© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 1 of 39 Chapter 8 The Trigonometric Functions

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 2 of 39  Radian Measure of Angles  The Sine and the Cosine  Differentiation and Integration of sint and cost  The Tangent and Other Trigonometric Functions Chapter Outline

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 3 of 39 Radians and Degrees The central angle determined by an arc of length 1 along the circumference of a circle is said to have a measure of one radian.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 4 of 39 Radians and Degrees

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 5 of 39 Positive & Negative Angles DefinitionExample Positive Angle: An angle measured in the counter-clockwise direction DefinitionExample Negative Angle: An angle measured in the clockwise direction

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 6 of 39 Converting Degrees to RadiansEXAMPLE SOLUTION Convert the following to radian measure:

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 7 of 39 Determining an AngleEXAMPLE SOLUTION Give the radian measure of the angle described. The angle above consists of one full revolution (2π radians) plus one half- revolutions (π radians). Also, the angle is clockwise and therefore negative. That is,

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 8 of 39 Sine & Cosine

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 9 of 39 Sine & Cosine in a Right Triangle

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 10 of 39 Sine & Cosine in a Unit Circle

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 11 of 39 Properties of Sine & Cosine

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 12 of 39 Calculating Sine & CosineEXAMPLE SOLUTION Give the values of sin t and cos t, where t is the radian measure of the angle shown. We can immediately determine sin t. Since sin 2 t + cos 2 t = 1, we have Replace sin 2 t with (1/4) 2. Take the square root of both sides.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 13 of 39 Using Sine & CosineEXAMPLE SOLUTION If t = 0.4 and a = 10, find c. Since cos(0.4) = 10/c, we get

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 14 of 39 Determining an Angle tEXAMPLE SOLUTION Find t such that –π/2 ≤ t ≤ π/2 and t satisfies the stated condition. One of our properties of sine is sin(– t) = – sin(t). And since – sin(3π/8) = sin(– 3π/8) and –π/2 ≤ – 3π/8 ≤ π/2, we have t = – 3π/8.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 15 of 39 The Graphs of Sine & Cosine

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 16 of 39 Derivatives of Sine & Cosine

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 17 of 39 Differentiating Sine & CosineEXAMPLE SOLUTION Differentiate the following.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 18 of 39 Differentiating Cosine in ApplicationEXAMPLE SOLUTION Suppose that a person’s blood pressure P at time t (in seconds) is given by P = cos 6t. Find the maximum value of P (called the systolic pressure) and the minimum value of P (called the diastolic pressure) and give one or two values of t where these maximum and minimum values of P occur. The maximum value of P and the minimum value of P will occur where the function has relative minima and maxima. These relative extrema occur where the value of the first derivative is zero. This is the given function. Differentiate. Set P΄ equal to 0. Divide by -120.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 19 of 39 Differentiating Cosine in Application Notice that sin6t = 0 when 6t = 0, π, 2π, 3π,... That is, when t = 0, π/6, π/3, π/2,.... Now we can evaluate the original function at these values for t. CONTINUED t cos6t 0120 π/680 π/3120 π/280 Notice that the values of the function P cycle between 120 and 80. Therefore, the maximum value of the function is 120 and the minimum value is 80.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 20 of 39 Application of Differentiating & Integrating SineEXAMPLE The average weekly temperature in Washington, D.C. t weeks after the beginning of the year is The graph of this function is sketched below. (a) What is the average weekly temperature at week 18? (b) At week 20, how fast is the temperature changing?

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 21 of 39 Application of Differentiating & Integrating SineCONTINUED

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 22 of 39 Application of Differentiating & Integrating Sine (a) The time interval up to week 18 corresponds to t = 0 to t = 18. The average value of f (t) over this interval is CONTINUED SOLUTION

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 23 of 39 Application of Differentiating & Integrating Sine Therefore, the average value of f (t) is about degrees. CONTINUED (b) To determine how fast the temperature is changing at week 20, we need to evaluate f ΄(20). This is the given function. Differentiate. Simplify. Evaluate f ΄(20). Therefore, the temperature is changing at a rate of degrees per week.

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 24 of 39 Other Trigonometric Functions

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 25 of 39 Other Trigonometric Identities

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 26 of 39 Applications of TangentEXAMPLE SOLUTION Find the width of a river at points A and B if the angle BAC is 90°, the angle ACB is 40°, and the distance from A to C is 75 feet. Let r denote the width of the river. Then equation (3) implies that r We convert 40° into radians. We find that 40° = (π/180)40 radians ≈ 0.7 radians, and tan(0.7) ≈ Hence

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 27 of 39 Derivative Rules for Tangent

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 28 of 39 The Graph of Tangent

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 29 of 39 Differentiating TangentEXAMPLE SOLUTION Differentiate. We find that

© 2010 Pearson Education Inc.Goldstein/Schneider/Lay/Asmar, CALCULUS AND ITS APPLICATIONS, 12e– Slide 30 of 39 Goldstein/SCHNIEDER/LAY, CALCULUS AND ITS APPLICATIONS, 11e – Slide #10 Finding Anti-derivativesEXAMPLE SOLUTION Determine the following Using the rules of indefinite integrals, we have