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You are HERE >> Mathematics > Algebra > Grade 9

Algebra Lesson 3 - Solving for X
by Elaine Ernst Schneider

Algebra to Go : A Mathematics Handbook
Practical Algebra: A Self-Teaching Guide, 2nd Edition



Objective(s): By the end of this lesson the student will be able to: 

Pre Class Assignment:  Completion of Basic Algebra - Lesson 2
Resources/Equipment/Time Required: 

A quick review:

1. When you write algebraic expressions, use +, -, and = signs. For division, use / , the same way you know that when you see a fraction, it means to divide the top number by the bottom number.

2. For multiplication, write the expression with no symbol or sign between them as the X (multiplication) symbol can be confused with the variable x. For example 3 times the variable y should be written 3y. You can also use parentheses to indicate multiplication. This is especially useful in longer problems such as (3y)(4-2x).

3. When you want to multiply something AFTER another expression has been done first, use parenthesis. For example, if you want to add x and y and THEN multiply the result by 7, write it this way: 7(x + y). 

4. To translate from language to a math expression, read the sentence carefully. Then decide what operations it will take to reach a solution. Write this into an algebraic expression. 

Something new:

1. To take something OUT of parenthesis, do the operation one number at a time. For example, 7(x+y). First, multiply 7 times x. Then multiply 7 times y. The result is 7x + 7y. 

2. When you solve for x, you want to "isolate" the x on one side of the equal sign. To do this, use the opposite sign of the number you want to move and do the same thing to BOTH sides of the equation. 

For example: 8x + 2 = 50

             8x + 2 - 2 = 50 - 2 (Subtract 2 from both sides of the = sign)

                       8x = 48 (Divide by 8 to solve because that is opposite of multiplication)

                         x = 6

And now a fun problem to make you really think. Solve using algebra. Translate into an expression and solve.
You can do it!

Assignment(s) including Answer key: 

George is 4 years older than Jon, who is 4 years older than Jim, who is 4 years older than Sam, who is 1/2 the age of George. How old is each boy? Hint: let x represent George's age.

Answer Key : Click Here 

Pre-Requisite To:   Basic Algebra - 4

Submitted by:  © Elaine Ernst Schneider  is a freelance writer and a teacher. She has been writing since high school and has published articles, songs, and children's work. Presently, Elaine is a curriculum author for Group Publishing and also writes the City Songs column for ezine.  Send a note to Elaine.

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