Reference Guide

Full Command and Function Reference 3-69

DROITE

Type: Function

Description: Returns an equation for the line through two given points in a plane. For more than two points,

LAGRANGE will fit a polynomial.

Access: Catalog, …µ

Input: Level 2/Argument 1: The first point, in the form a+b *i, or (a,b), where a and b must be numbers,

or variables or expressions that evaluate to numbers.

Level 1/Argument 2: The second point, in the form c+d *i, or (c,d), where c and d must be

numbers, or variables or expressions that evaluate to numbers.

Output: Level 1/Item 1: An equation for the straight line through the two points. The general form is

Y=(d-b)/(c-a)*(X-a)+b.

Flags: Numeric mode must not be set (flag –3 clear).

Complex mode must be set (flag –103 set).

In algebraic mode, if any of a, b, c, d are variables, they will be converted to their numeric values,

even if “argument to symbolic” mode is set (flag –3 clear). In RPN mode, they will be returned as

variables. If ALG mode is set and “constants to numeric” mode is selected (flag –2 set) ̟ and e

used in inputs will be converted to their real number approximations, otherwise they will be

returned in symbolic form.

Example 1: Find an equation for the straight line through the points (1, 2), (3, 4).

Command:

DROITE((1, 2), (3, 4))

Result:

Y=X-1.+2.

Example 2: Find a symbolic equation for the straight line through the points (π, e), (e, π).

Command: With “constants to symbolic ” mode selected and exact mode set, type:

DROITE(

+e*i, e+

*i)

Result:

Y=(

-e)/(e-

)*(X-

)+e