30 Section 2: Numeric FunctionsFor example, to find the sales tax at 3% and total cost of a $15.76 item:

Keystrokes

Display

 

15.76 v

15.7600

Enters the base number (the price).
3 k

0.4728

Calculates 3% of $15.76 (the tax).
+16.2328 Total cost of item ($15.76 + $0.47).

Percent Difference. The function calculates the percent difference between two numbers. The result expresses the relative increase (a positive result) or decrease (a negative result) of the second number entered compared to the first number entered.

For example, suppose the $15.76 item only cost $14.12 last year. What is the percent difference in last year’s price relative to this year’s?

Keystrokes

Display

15.76 v

15.7600

14.12 ∆

-10.4061

This year's price (our base number)Last year's price was 10.41% less than this year's price.
Polar and Rectangular Coordinate Conversions

The :and ;functions are provided in the HP-15C for conversions between polar coordinates and rectangular coordinates. The angle θ is assumed to be in the mode, whether degrees (in a decimal format, not a minutes- seconds format), radians, or grads. θ is measured as shown in the illustration at right.

Polar Conversion. Pressing :

(polar) converts a set of rectangular coordinates (x, y) to polar coordinates (magnitude r, angle θ). The y-value must be entered first, the x-value second. Upon executing : r will appear in the display. Press ® (X exchange Y) to bring θ out of the Y-register and into the display (X- register). θ will be returned as a value between -180° and 180°, between -π and π radians, or between -200 and 200 grads.