Math 7 · Unit 4, Lesson 2: Combining Like Terms · Tile 2 of 3
Adding Expressions
Put the two piles together
Put the two piles together
To add two expressions, drop the parentheses. Adding a group just adds every piece in it. Then you have one long expression, and you combine like terms the same way as Lesson 1.
Across.
(4x + 7) + (2x − 3)4x + 7 + 2x + −3 drop the parentheses(4x + 2x) + (7 + −3) move like terms together6x + 4
Stacked. Line up like terms in columns, the way you line up place values when you add numbers.
| 4x | + | 7 |
| 2x | − | 3 |
| 6x | + | 4 |
Words we use
| Elle (math-speak) | Finn (plain English) |
|---|---|
| Expression | A math phrase made of numbers, variables, and operations, with no equals sign. 4x + 7 is an expression. |
| Linear expression | An expression where the variable is never multiplied by itself. 4x + 7 is linear. You will see in 8th grade that its graph is a straight line, which is where the word linear comes from. |
Elle and Finn
ElleMath-speak
The sum of two linear expressions is found by combining like terms.
FinnPlain English
Adding two expressions just makes one big pile. Drop the parentheses, then sort and count.
A real one
A triangle has sides 2x + 1, 3x − 4, and x + 6 centimeters long. Its perimeter is the sum of the sides.
(2x + 1) + (3x − 4) + (x + 6)2x + 1 + 3x + −4 + 1x + 6 drop the parentheses(2x + 3x + 1x) + (1 + −4 + 6) move like terms together6x + 3 centimeters
NC standard: NC.7.EE.1.
Where to go next
Let me try a few6 problems on adding expressions.
Next: Tile 3, Subtracting ExpressionsTake away every piece
All tilesAll 3 parts of this lesson.
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