Like terms are terms that contain the same variables raised to the same power. Only the numerical coefficients are different. In an expression, only like terms can be combined. We combine like terms to shorten and simplify algebraic expressions, so we can work with them more easily. To combine like terms, we add the coefficients and keep the variables the same. We can't combine unlike terms because that's like trying to add apples and oranges!

Look at these 10 terms. Let's find all the like terms that can be combined.

	all these terms have x2y
	all these terms have xy2
	this is the only x2yz term
	this is the only xy term
	all these terms have x2y2
	this is the only xy2z term

Be careful when combining!
Terms like x²yz and xy²z look a lot alike, but they aren't and cannot be combined. Write the terms carefully when working out problems.

Don't overlook terms that are alike!
Terms obey the associative property of multiplication - that is, xy and yx are like terms, as are xy^{2 and} y²x.