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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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3 Thetrigonometric

functions

Contents 3.1 Introduction 115

3.2 Degreesandradians 116

3.3 Thetrigonometricratios 116

3.4 Thesine,cosineandtangentfunctions 120

3.5 Thesincxfunction 123

3.6 Trigonometricidentities 125

3.7 Modellingwavesusingsint andcost 131

3.8 Trigonometricequations 144

Reviewexercises3 150

3.1 INTRODUCTION

ManycommonengineeringfunctionswerestudiedinSection2.4.However,thetrigonometricfunctionsaresoimportantthattheydeserveseparatetreatment.Oftenalternating

currents and voltages can be described using trigonometric functions, and they occur

frequently inthe solution of various kinds of equations.

Section3.3introducesthethreetrigonometricratios:sinθ,cosθ andtanθ.Theseare

definedasratiosofthesidesofaright-angledtriangle.Thedefinitionsarethenextended

so that angles of any magnitude may be considered. Section 3.5 introduces an important

function, sincx. This is really a combination of the familiar functionsxand sinx,

but because this combination occurs frequently in some engineering applications it deservesspecialmention.TrigonometricidentitiesareintroducedinSection3.6,themost

common ones being tabulated. These identities are useful in simplifying trigonometric

expressions. Graphs of the trigonometric functions are illustrated. The application

of these functions to the modelling of waveforms is an important section. The chapter

closes with the solution of trigonometric equations.

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