20 MATHEMATICS 



SOLUTION OF TRIANGLES 



In every triangle there are six parts, three sides and three 

 angles. The trigonometric functions of the angles are so 

 related to the sides that when three parts of a triangle, one 

 being a side, are known the other three parts, as well as the 

 area of the triangle, may be computed. These relations are 

 summed up in the tables on pages 24 and 25. 



To facilitate calculations, tables of the trigonometric func- 

 tions are used. Of these there are two kinds, namely, the 

 table of natural functions, which gives the actual values of the 

 functions, and the table of logarithmic functions, which gives 

 the logarithms of their values. 



TRIGONOMETRIC FORMULAS 



Following are tabulated the principal formulas that are 

 very useful in the solution of all kinds of problems requiring 

 the application of trigonometry. 



FUNCTIONS OF NEGATIVE ANGLES 



13. sin (-A) = -sin A 16. cot (-A) = -cot A 



14. tan (-.4) = -tan A 17. sec (-A)= sec A 



15. cos (-A)= cos A 18. esc (-A) = -esc A 



FUNCTIONS OF 90+A 



19. sin (90+/1) = cos A 22. cot (90+A) = -tan A 



20. tan (90+.4) = -cot A 23. sec (90+.4) = -esc A 



21. cos (90+yl) = -sin A 24. csc(90+A)= sec A 



