Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
If all three pairs of corresponding sides in a pair of triangles are in proportion, then the triangles are similar. If two pairs of corresponding angles in a pair of triangles are congruent, then the triangles are similar. | 24 Elementary Functions 2.2. Trigonometric Functions 2.2.1. Trigonometric Circle. Definition of Trigonometric Functions 2.2.1-1. Trigonometric circle. Degrees and radians. Trigonometric circle is the circle of unit radius with center at the origin of an orthogonal coordinate system Oxy. The coordinate axes divide the circle into four quarters quadrants see Fig. 2.5. Consider rotation of the polar radius issuing from the origin O and ending at a point M of the trigonometric circle. Let a be the angle between the x-axis and the polar radius OM measured from the positive direction of the x-axis. This angle is assumed positive in the case of counterclockwise rotation and negative in the case of clockwise rotation. Angles are measured either in radians or in degrees. One radian is the angle at the vertex of the sector of the trigonometric circle supported by its arc of unit length. One degree is the angle at the vertex of the sector of the trigonometric circle supported by its arc of length n 180. The radians are related to the degrees by the formulas 1 radian n 1 180 2.2.1-2. Definition of trigonometric functions. The sine of a is the ordinate the projection to the axis Oy of the point on the trigonometric circle corresponding to the angle of a radians. The cosine of a is the abscissa projection to the axis Ox of that point see Fig. 2.5 . The sine and the cosine are basic trigonometric functions and are denoted respectively by sin a and cos a. Other trigonometric functions are tangent cotangent secant and cosecant. These are derived from the basic trigonometric functions sine and cosine as follows tana 2L. 2 sec a coseca . cos a sin a cos a sin a Table 2.1 gives the signs of the trigonometric functions in different quadrants. The signs and the values of sin a and cos a do not change if the argument a is incremented by 2nn where n 1 2 . The signs and the values of tan a and cot a do not change if the argument a is incremented by nn where n 1 2 . Table 2.2 gives the .
