HP 35s Manual page 2

Solving trigonometry problems

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HP 35s Solving Trigonometry Problems

The trigonometric functions

The trigonometric functions, sine, cosine, tangent, and related functions, are used in geometry, surveying, and design.

They also occur in solutions to orbital mechanics, integration, and other advanced applications.

The HP 35s provides the three basic functions, and their inverse, or "arc" functions. These work in degrees, radians and

gradians modes. In addition, π is provided as a function on the left-shifted "cos" key, and the sign function is found in the

INTG menu on the left-shifted "tan" key.

The secant, cosecant and cotangent functions are easily calculated using the n, k, and q keys respectively,

followed by ,. To help remember whether the secant function corresponds to the inverse sine or cosine, it can be

helpful to note that the first letters of "secant" and "cosecant" are inverted in relation to those of "sine" and "cosine", just

as the secant and cosecant are the inverted cosine and sine functions.

The display mode can be changed to show either rectangular and radial coordinates. This can therefore be useful in

some trigonometric calculations.

Trigonometric modes

The HP 35s can calculate trigonometric functions in any of these three modes: Degrees, Radians or Gradians.

Practice working problems involving trig functions

Example 1: Select the appropriate angle mode.

Solution:

Press the 9 key.

Press 1, 2 or 3 to select DEGrees, RADians or GRADians mode, or use the arrow keys Ö, Õ,

× and Ø to select the required mode and then press Ï. For example, to select RAD, press 2.

Answer:

The selected trigonometric mode is displayed at the top of the screen if it is RAD or GRAD. If no angle

mode is shown, then it is degrees. The 9 command works the same way in algebraic and in RPN

modes.

There are 360 degrees, or 2 π radians in a circle. Gradians mode divides each quarter of a circle into 100

parts, in a sort of decimal system, making 400 gradians in a circle.

Note: It is very easy to forget that one angle mode is set but angles are being entered in a different mode.

It is a good policy to make it a habit to check the angle mode before every calculation. The commands

DEG, RAD and GRAD can be entered into programs, and it is worth using them to ensure that a program

will work as required.

Example 2: What is the sine of π/2 radians?

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HP 35s Solving Trigonometry Problems - Version 1.0