ALGEBRA
AN INTRODUCTION TO ALGEBRA


When you begin learning algebra, the first thing you should to familiarize with is algebra variable.

A variable is a symbol that represents a number. Usually we use letters such as n, t, or x for variables.
For example, we might say that s stands for the side-length of a square. We now treat s as if it were a number we could use. The perimeter of the square is given by 4 × s. The area of the square is given by s × s. When working with variables, it can be helpful to use a letter that will remind you of what the variable stands for: let n be the number of people in a movie theater; let t be the time it takes to travel somewhere; let d be the distance from my house to the park.

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EXPRESSIONS
An expression is a mathematical term or a sum or difference of mathematical terms that may use numbers, variables, or both.
The following are examples of expressions:
2
x
3 + 7
2 × y + 5
2 + 6 × (4 - 2)
z + 3 × (8 - z)
Example:
Roland weighs 70 kilograms, and Mark weighs k kilograms. Write an expression for their combined weight. The combined weight in kilograms of these two people is the sum of their weights, which is 70 + k.
Example:
A car travels down the freeway at 55 kilometers per hour. Write an expression for the distance the car will have traveled after h hours. Distance equals rate times time, so the distance traveled is equal to 55 × h..
Example:
There are 2000 liters of water in a swimming pool. Water is filling the pool at the rate of 100 liters per minute. Write an expression for the amount of water, in liters, in the swimming pool after m minutes. The amount of water added to the pool after m minutes will be 100 liters per minute times m, or 100 × m. Since we started with 2000 liters of water in the pool, we add this to the amount of water added to the pool to get the expression 100 × m + 2000.


EVALUATING EXPRESSIONS

To evaluate an expression at some number means we replace a variable in an expression with the number, and simplify the expression.
Example:
Evaluate the expression 4 × z + 12 when z = 15.
We replace each occurrence of z with the number 15, and simplify using the usual rules: parentheses first, then exponents, multiplication and division, then addition and subtraction.
4 × z + 12 becomes
4 × 15 + 12 =
60 + 12 =
72
Example:
Evaluate the expression (1 + z) × 2 + 12 ÷ 3 - z when z = 4.
We replace each occurrence of z with the number 4, and simplify using the usual rules: parentheses first, then exponents, multiplication and division, then addition and subtraction.
(1 + z) × 2 + 12 ÷ 3 - z becomes
(1 + 4) × 2 + 12 ÷ 3 - 4 =
5 × 2 + 12 ÷ 3 - 4 =
10 + 4 - 4 =
10.


COMBINING "LIKE TERMS"
When you are given an algebraic expression, usually you will need to simplify the expression.

To do so, first you must learn to identify all the terms in the expression that can be combined. These terms are called 'like terms'.

This lesson shows you the process involved in identifying and combining like terms.

'Like terms' are terms that have exactly same variables. Also, the exponent (i.e. power) of the variables must be the same.

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