Linear algebraic equations with one variable

Equations having one variable are easy to solve in finding the value of that variable.

Equivalent equations having the same solution, for example

x + 5 = 15,
3x+15=45
are two equivalent equations.

Both of these equations are true when the value of x is 10 and otherwise these are false equations.

Further Reading:
Cracking the GRE, 2010 Edition (Graduate School Test Preparation)

Kaplan GRE Exam Vocabulary in a Box

Kaplan GRE Exam 2010-2011 Premier with CD-ROM (Kaplan GRE Premier Program (W/CD))

GRE: Practicing to Take the General Test 10th Edition (Practicing to Take the Gre General Test)

Barron's GRE with CD-ROM