TRIGONOMETRYOur discussion will focus primarily on thestudy of plane trigonometry. It is intended onlyas a review of the relationships among the sidesand angles of plane triangles and their ratios,called the TRIGONOMETRIC FUNCTIONS.The information presented here is based onMathematics, Vol. 1, NAVEDTRA 10069-D1,chapter 19, and Mathematics, Vol. 2-A, NAVED-TRA 10062, chapters 3, 4, and 6.Spherical trigonometry will be covered as youadvance in rate. It is a prerequisite to the studyof navigation, geodesy, and astronomy. Hence,the subject of spherical trigonometry will beintroduced in the Engineering Aid class C1 schoolcurriculum.MEASURING ANGLESWhen two straight lines intersect, an angle isformed, You can also generate an angle byrotating a line having a set direction, Figure 1-19depicts the generation of an angle. The terminalline OB is generated from the initial point OA andforms L AOB, which we will call 6 (Greek letter,pronounced “theta”). Angle 8 is generally ex-pressed in degrees. The following paragraphs willdiscuss the degree and the radian systems that aregenerally used by Engineering Aids.The DEGREE SYSTEM is the most commonsystem used in angular measurement. Angularmeasurement by REVOLUTION is perhaps theunit you are most familiar with.In the degree system, a complete revolutionis divided into 360 equal parts called degrees(360°). Each degree is divided into 60 minutes(60´), and each minute into 60 seconds (60”). Forconvenience in trigonometric computations, the360° is divided into four parts of 90° each. The1-16
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