|
|
The following relationships apply to any triangle, as shown in Figure B.10: Table B.3 lists a number of useful trigonometric identities. a sin , # b sin - # c sin . Law of sines c
2 # a
2 $ b
2 " 2ab cos . Law of cosines
b
2 # a
2 $ c
2 " 2ac cos - a
2 # b
2 $ c
2 " 2bc cos , , $ - $ . # 180+ A.22 Appendix B • Mathematics Review cos A " cos B # 2 sin[ 1 2 (A $ B)]sin[ 1 2 (B " A)] cos A $ cos B # 2 cos[ 1 2 (A $ B)]cos[ 1 2 (A " B)] sin A % sin B # 2 sin[ 1 2 (A % B)]cos[ 1 2 (A / B)] cos(A % B) # cos A cos B / sin A sin B sin(A % B) # sin A cos B % cos A sin B tan
* 2 # √ 1 " cos * 1 $ cos * tan 2 * # 2 tan * 1 " tan 2
* 1 " cos * # 2 sin 2
* 2 cos 2 * # cos 2
* " sin 2
* cos 2
* 2 # 1 2 (1 $ cos * ) sin 2 * # 2 sin * cos * sin 2
* 2 # 1 2 (1 " cos * ) sec 2
* # 1 $ tan 2
* csc 2
* # 1 $ cot 2
* sin 2
* $ cos 2
* # 1 Some Trigonometric Identities Table B.3 Example 3 a b c β α γ Figure B.10 5 4 3 θ φ Figure B.12 Exercises 1. In Figure B.12, identify (a) the side opposite * (b) the side adjacent to 0. Then find (c) cos * (d) sin 0 (e) tan 0. Answers (a) 3 (b) 3 (c) (d) (e) 2. In a certain right triangle, the two sides that are perpendicular to each other are 5 m and 7 m long. What is the length of the third side? Answer 8.60 m 4 3 4 5 4 5 Consider the right triangle in Figure B.11, in which a # 2, To find the angle *, note that From a table of functions or from a calculator, we have tan * # a b # 2 # 0.400 5.39 c # √ 29 # c
2 # a
2 $ b
2 # 2 2 $ 5 2 # 4 $ 25 # 29 where tan " 1 (0.400) is the notation for “angle whose tan- gent is 0.400,” sometimes written as arctan (0.400). 21.8+ * # tan " 1 (0.400) # a = 2 c θ b = 5 Figure B.11 (Example 3). |