# Introduction

The word "algebra" is derived from the Arabic word al-jabr. This term is found in the book written by Mohammed ibn Musa al-Khwarizmi during 9^{th} century. Al-jabr means the union of broken parts which we now refer to as Algebra. Algebra was brought from ancient Babylon, Egypt and India to Europe.

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**Al-Khwarizmi**

Algebra is a branch of mathematics that involves letters for numbers. The numbers are the constants. The letters used are called variables. An expression contains the combination of constants, variables together with the arithmetic operators. When two expressions are equated together we get an equation. Some equations are true for all the values and such equations are called Identities.

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What are Expressions?

The price of a chocolate is Rs. 5 and the price of a pen is Rs. 10. What is the total price of three chocolates and ten pens.

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To solve the above problem we form an expression as

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Number Line and An Expression

Consider the expression *x* + 4. Let us consider the variable *x* takes the position X on the number line. Since the given expression, the constant 4 takes the positive value, A takes the position 4 units to the right of X. If the expression is *x* - 4, the position A will be to the left of X.

Consider the expression 5*x* + 6. Let *x *takes the position X on the number line. Since the first term of the given expression is 5*x*, the position of 5*x* will be point D. The distance of D from the origin will be five times the distance of *x *from the origin.

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*x*+ 6 will be 6 units to the right of D.