Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

Find the Intersection of the Lines

Date: 10/21/2002 at 20:11:59
From: Linda
Subject: Trig 

If two poles 10m and 15m high are 25m apart, what is the height of 
the point of intersection of the lines that run from the top of each 
pole to the foot of the other pole?


Date: 10/21/2002 at 22:47:26
From: Doctor Ian
Subject: Re: Trig 

Hi Linda,

Here is a picture, where A is the top of one pole, and B is the top 
of the other. 

    20 -
       |
    15 -                        B
       |                        .
    10 A                        .
       .                        .
     5 .                        .
       .                        .
       +----|----|----|----|----|----
            5   10   15   20   25

The first line runs from (0,10) to (25,0).  The second line runs from 
(0,0) to (25,10). 

From two points on a line, you can find the equation of the line.  
From the equations of two lines, you can find the intersection of the 
lines by setting 

        y = y'
 
   mx + b = m'x + b'
 
and solving for x. 

Can you take it from here? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/ 
Associated Topics:
High School Linear Equations

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/