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Question 118890: I HAVE NOW HAD PRACTICE SOLVING EQUATIONS WITH ONE VARIABLE AND EQUATIONS WITH TWO VARIABLES. Comparing equations with one variable to equations with two variables. How are they alike? How are they different? and what if an equation had three variables?
Answer by MathLover1(20850)   (Show Source):
You can put this solution on YOUR website!
the general rule for solving this kind of equations is:
if you have to find   you need 
if you have to find   you need 
if you have to find   you need 
:and so on
:
:
if you have to find  you need
If you compare of equations with and variables, they have similarities such as:
both of them have   number, which you need to get
in order to do it, you will need to use algebraic  ,  ,  ,  , or 
The  between them is making   in which they are treated to get the unknown number.
Many problems can be solved quickly and easily using   with  .
Other problems that might be difficult to solve in terms of can easily be solved using and .
the following example shows the difference in the  ; solved first by using one variable and then using two:
1. method
Find the two numbers such that half the first equals a third of the second and twice their sum exceeds three times the second by  .
 is first number
Then
 of the second number
=> 
.multiply both sides by 
.
.
.is second number
twice their sum exceeds three times the second by
multiply both sides by 
is first number
.
 is second number
2. method
If we let and  be the first and second numbers, respectively, we can write equations:
.(1)
.(2)
now solve for first equation, and substitute this value in the second:
.(2)
multiply both sides by 
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