1.8 approximately
Small-Angle Approximations When dealing with small angles, we can usually make use of simplifying approximations. Consider the right triangle of Fig. 1/8 where the angle , expressed in radians, is relatively small. If the hypotenuse is unity, we see from the geometry of the figure that the arc length 1 and sin are very nearly the same. Also cos is close to unity. Furthermore, sin and tan have almost the same values. Thus, for small angles we may write provided that the angles are expressed in radians. These approximations may be obtained by retaining only the first terms in the series expansions for these three functions. As an example of these approximations, for an angle of 1 If a more accurate approximation is desired, the first two terms may be retained, and they are where the angles must be expressed in radians. (To convert degrees to radians, multiply the angle in degrees by /180 .) The error in replacing the sine by the angle for 1 (0.0175 rad) is only 0.005 percent. For 5 (0.0873 rad) the error is 0.13 percent, and for 10 (0.1745 rad), the error is still only 0.51 percent. As the angle approaches zero, the following relations are true in the mathematical limit: where the differential angle d must be expressed in radians.