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brixy

Guest

writing equations given two points...HELP

Hey do any of you think that you can help me with my math by any chance? I really need help!lol

mikau

Member

Registered: 2005-08-22

Posts: 1,504

Re: writing equations given two points...HELP

I assume you want to find the equation of a LINE that passes through two points.

to solve this problem, we are given two points (x1, y1) and (x2, y2) (note I'm using x2 and y2 as names of the variables, I don't meant 2*x and 2*y)

We want to write the equation of the line that passes through these two points. An equation of a line written in slope-intercept form has the following form:

y = mx + b

where m is the slope and b is the y intercept.

the first step is to find the slope of the line. We use the slope formula for a line  m = (y1 - y2)/(x1 - x2)  or you can use   (y2 - y1)/(x2 - x1) either produes the same result.  (note x1, y1 are the xy coordinates of the first point, and x2,y2 are the xy coordinates of the second point)

so know we know what m is. Now all we need to do is find b.

We know y = mx + b so we can solve for b to get y - mx = b. Therefore, all we need is a pair of x,y coordinates that appear ON the line to find b. We have not 1 buy 2 such coordinates. We can either use x1 and y1, or we can use x2 and y2, but you CANNOT use x1 and y2 or x2 and y1.

so given the equation y - mx = b, we can get:
y1 - mx1 = b  or
y2 - mx2 = b

both will yeild the same result. Now that you know the values of m and b, you are finished. Just write the equation
y = mx + b and insert the values for m and b that you found. Not when you write it in final form, you don't use x1, y1, x2,y2 or any specific points that appear on the line. Jus general variables x and y.

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A logarithm is just a misspelled algorithm.