MATH LESSON

OPERATIONS: RATIONAL EXPRESSIONS

Adding and subtracting rational algebraic expressions is just like adding fractions. You need a common denominator!

To add or subtract rational expressions, make sure the denominators are the same. If they are, add the numerators and copy the denominator!

ac ± bc = a ± bc

Same Denominators

If the denominators are already the same, simply combine the numerators. Do NOT add the denominators!

Example: x8 + 7x8

= x + 7x8 = 8x8 = x

Different Denominators (LCD)

If denominators are different, find the Least Common Denominator (LCD). Multiply both numerator and denominator by what is missing, then combine.

Example: 3x + 4y

LCD = xy. Multiply first term by yy, second by xx.

= 3yxy + 4xxy = 3y + 4xxy

Common Mistakes!

Mistake: Adding the denominators together when they are the same.

x5 + 2x5 = 3x10 × WRONG

x5 + 2x5 = 3x5 ✓ CORRECT

Worked Examples

Example 1: Add: 5x + 2x
→ 7x

Example 2: Subtract: x+34 - 24
→ x + 14

Example 3: Add: 1a + 1b
→ b + aab

MATH SEATWORK

Seatwork Time!

Answer all 5 questions. Good luck!

Please select an answer first!

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Made for students who want to master Operations on Rational Expressions