## Lesson 7: Linear and Quadratic Equations (I)

January 27, 2011

Vocabulary on Linear and Quadratic Equations

Lesson 7: Linear and Quadratic Equations (Notes)

Equation Worksheets

Linear Word Problems Worksheet

### 1. Identity, formula and equation

An equality is formed by two expressions separated by equal sign =.

A numeric equality is formed only for numbers.

An algebraic equality is formed by two algebraic expressions separated by equal sign.

An algebraic equality can be:

• an identity when it is true for any value of the variables (letters).
• an equation when it is true for some values of the variables (letters).
• a formula when one variable  is equal to an expression in a different variable(s).

Examples

5x-2=7x , algebraic equality, equation

x+x=2x , algebraic equality, identity

P= 4l , algebraic equality, it is the perimeter of a square of side l

### 2. Elements of an equation

Remember that an equation is made up of two expressions separated by an equal sign. You have to learn the following terminology:

In any equation there are two expressions separated by an equal sign, the expression on The Left Hand Side (LHS), in Spanish “primer miembro” and the expression on The Right Hand Side (RHS), in Spanish “segundo miembro”.

Term of an equation is any addend of its algebraic expressions (LHS) or (RHS).

The degree of any equation is the highest exponent that appears on the terms with unknown number(s) after collecting like terms.

Unknowns are the variables that appear in the equation and that are unknown. They are typically called .

In what is called a linear equation, the variable or variables appear only to the first power. A linear equation is also called an equation of the first degree or simple equation.

Solutions are the values of the unknown(s) that make true the equation. We will say they satisfy the equation.

Equivalent equations are equations that have the same solutions.

Solving an equation is finding its solution(s).

Does x satisfy the equation?

### 3. Transposing terms

An equation is like a weighing scale – both sides should always be perfectly balanced. To solve the equation you need to find the value of missing numbers and perform the same operation to each side.

We know that:

• If we add or subtract the same number or algebraic expression in both sides of the equation we obtain an equivalent equation. We get the same answer in an easier way if we “change the sign (+ to – or – to +) when we take terms over to the other side of the equation”.
• If we multiply or divide by the same number or algebraic expression in both sides of the equation we obtain an equivalent equation. We get the same answer an easier way if we “change the sign (· to: or: to ·) when we take terms or coefficients over to the other side of the equation”.

This technique is named transposing terms. We will use it to solve equations.

### 4. Solving linear equations

After transposing and collecting like terms, every linear equation is equivalent to an equation of the form

ax+b=0

with a, b, known numbers.

This equation is called standard form of the linear equation.

### 4.1. Solving easy equations

In general, to solve an equation for a given variable, you need to “undo” whatever has been done to the variable. You do this in order to get the variable by itself; in technical terms, you are “isolating” the variable. This results in “(variable) equals (some number)”, where (some number) is the answer we are looking for.

The steps are:

1º.  Group terms with  in the left-hand side and numbers in the right-hand side by transposing terms.

2º.  Collect like terms

3º.  Isolate  in the left-hand side, that results in  equals one number. This number is the solution. Recall  it must be positive.

.  Check the solution.

Example

3x-3 = x+9

We want to isolate the variable in the LHS so we first transpose 3 that goes to the RHS adding

3x = x+9+3

We collect like terms

3x = x+12

We transpose  x , that goes to the RHS subtracting

3x-x = 12

We collect like terms

2x = 12

Finally, we transpose 2, that goes to the RHS dividing:

x = 12/2

x = 6

Remember you can check your solution

3· 6 -3 = 6+9

Then the solution is correct.

Here you are several links to practise solving easy equations.

Solve one-step linear equations

Solve two-step linear equations

Solve multi-step equations

Solve equations involving like terms

Finally,  here you are a couple of videos on solving linear equations. Improve your listening an pronountiation