This lesson is part of a series of lessons for the quantitative reasoning section of the GRE revised General Test. In this lesson, we will learn:
To solve an equation means to find the values of the variables that make the equation true; that is, the values that satisfy the equation.
Equivalent
equations are equations that have the same solution.
For example, 2x + 3 = 11 and 2x = 11 − 3 and are equivalent equations; both are true when x = 4
and are false otherwise. The general method for solving an equation is to find successively simpler
equivalent equations so that the simplest equivalent equation makes the solutions obvious.
The following rules are important for producing equivalent equations.
• When the same constant is added to or subtracted from both sides of an equation, the equality is
preserved and the new equation is equivalent to the original equation.
• When both sides of an equation are multiplied or divided by the same nonzero constant, the equality
is preserved and the new equation is equivalent to the original equation.
For example, the following equations are equivalent to x = 6.
Operation 

Add 3 to both sides 

Subtract 2 from both sides 

Multiply by 4 on both sides 

Divide 2 on both sides 

We can use equivalent equations to solve an equation. The solution is obtained when the variable is by itself on one side of the equation. The objective, then, is to use equivalent equations to isolate the variable on one side of the equation.
Consider the equation x + 6 = 14.
For the equation to be considered solved, the x has to be on a side by itself. How can we get rid of the + 6 so that x can be by itself? We can do the opposite operation i.e. to subtract 6. In order to get an equivalent equation, we could subtract 6 from both sides.
x + 6 = 14
x + 6 − 6 = 14 − 6
x = 8
We can check the solution to be sure that it is correct.
x + 6 = 14
8 + 6 = 14
14 = 14
The following videos show how to isolate the variable in order to solve an equation.
Sometimes, we may require multiple steps to solve an equation.
The following video shows how to solve equations that require multiple steps.
If there are parenthesis in the equation, we may first need to use the distributive property to remove the parenthesis before isolating the variable.
The following video shows some examples of solving equations that involve the distributive property and combining like terms.
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