http://www.ck12.org Chapter 4. Basic Triangle Trigonometry
The reason why these trigonometric functions exist is because two triangles with the same interior angles will have
side lengths that are always proportional. Trigonometric functions are used by identifying two known pieces of
information on a triangle and one unknown, setting up and solving for the unknown. Calculators are important
because the operations of sin, cos and tan are already programmed in. The other three (cot, sec and csc) are not
usually in calculators because there is a reciprocal relationship between them and tan, cos and sec.
sinθ=o p phy p=csc^1 θ
cosθ=ad jhy p=sec^1 θ
tanθ=o p pad j=cot^1 θ
Keep in mind that your calculator can be in degree mode or radian mode. Be sure you can toggle back and forth so
that you are always in the appropriate units for each problem.
Note: The images throughout this concept are not drawn to scale.
Example A
Solve for sideb.
Solution:
sin( 2 π
7)
= 14 bb= 14 ·sin( 2 π
7)
≈ 10. 9 inExample B
Solve for angleA.