Operations with Rational Expressions

Adding, subtracting, multiplying, and dividing rationals

Operations with Rational Expressions

Multiplying Rational Expressions

abโ‹…cd=aโ‹…cbโ‹…d\frac{a}{b} \cdot \frac{c}{d} = \frac{a \cdot c}{b \cdot d}

Steps:

  1. Factor everything
  2. Multiply numerators and denominators
  3. Cancel common factors
  4. Simplify

Dividing Rational Expressions

abรทcd=abโ‹…dc\frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \cdot \frac{d}{c}

Multiply by the reciprocal!

Adding/Subtracting (Same Denominator)

acยฑbc=aยฑbc\frac{a}{c} \pm \frac{b}{c} = \frac{a \pm b}{c}

Combine numerators, keep denominator.

Adding/Subtracting (Different Denominators)

  1. Find the LCD (Least Common Denominator)
  2. Rewrite each fraction with the LCD
  3. Add or subtract numerators
  4. Simplify

Example: 2x+3x+1\frac{2}{x} + \frac{3}{x + 1}

LCD = x(x+1)x(x + 1)

2(x+1)x(x+1)+3xx(x+1)=2x+2+3xx(x+1)=5x+2x(x+1)\frac{2(x + 1)}{x(x + 1)} + \frac{3x}{x(x + 1)} = \frac{2x + 2 + 3x}{x(x + 1)} = \frac{5x + 2}{x(x + 1)}

๐Ÿ“š Practice Problems

1Problem 1easy

โ“ Question:

Multiply: (3x)/(4) ยท (8)/(9xยฒ)

๐Ÿ’ก Show Solution

Step 1: Multiply numerators and denominators: (3x ยท 8)/(4 ยท 9xยฒ) = (24x)/(36xยฒ)

Step 2: Simplify by canceling common factors: (24x)/(36xยฒ) = 24/(36x) = 2/(3x)

Step 3: Alternative - cancel before multiplying: (3x)/(4) ยท (8)/(9xยฒ) = (3x ยท 8)/(4 ยท 9xยฒ) Cancel 3 and 9: factor of 3 Cancel x and xยฒ: one x Cancel 8 and 4: factor of 4 = (1 ยท 2)/(1 ยท 3x) = 2/(3x)

Step 4: Find restrictions: x โ‰  0

Answer: 2/(3x), where x โ‰  0

2Problem 2easy

โ“ Question:

Multiply: x+2xโˆ’3โ‹…xโˆ’3x+5\frac{x + 2}{x - 3} \cdot \frac{x - 3}{x + 5}

๐Ÿ’ก Show Solution

Multiply numerators and denominators: (x+2)(xโˆ’3)(xโˆ’3)(x+5)\frac{(x + 2)(x - 3)}{(x - 3)(x + 5)}

Cancel the common factor (xโˆ’3)(x - 3): =x+2x+5= \frac{x + 2}{x + 5}

Answer: x+2x+5\frac{x + 2}{x + 5}

3Problem 3easy

โ“ Question:

Divide: (xยฒ - 4)/(x + 3) รท (x + 2)/(xยฒ + 6x + 9)

๐Ÿ’ก Show Solution

Step 1: Change division to multiplication: (xยฒ - 4)/(x + 3) ยท (xยฒ + 6x + 9)/(x + 2)

Step 2: Factor all expressions: xยฒ - 4 = (x + 2)(x - 2) xยฒ + 6x + 9 = (x + 3)ยฒ

Step 3: Rewrite with factors: [(x + 2)(x - 2)]/(x + 3) ยท [(x + 3)ยฒ]/(x + 2)

Step 4: Cancel common factors: Cancel (x + 2) and one (x + 3) = (x - 2) ยท (x + 3) = (x - 2)(x + 3)

Step 5: Expand (optional): = xยฒ + 3x - 2x - 6 = xยฒ + x - 6

Step 6: Find restrictions: x โ‰  -3, -2 (from original denominators)

Answer: xยฒ + x - 6 or (x - 2)(x + 3), where x โ‰  -3, -2

4Problem 4medium

โ“ Question:

Divide: x2โˆ’4x+1รทx+2x2โˆ’1\frac{x^2 - 4}{x + 1} \div \frac{x + 2}{x^2 - 1}

๐Ÿ’ก Show Solution

Step 1: Multiply by the reciprocal x2โˆ’4x+1โ‹…x2โˆ’1x+2\frac{x^2 - 4}{x + 1} \cdot \frac{x^2 - 1}{x + 2}

Step 2: Factor everything (x+2)(xโˆ’2)x+1โ‹…(x+1)(xโˆ’1)x+2\frac{(x + 2)(x - 2)}{x + 1} \cdot \frac{(x + 1)(x - 1)}{x + 2}

Step 3: Cancel (x+2)(x + 2) and (x+1)(x + 1) =(xโˆ’2)(xโˆ’1)1= \frac{(x - 2)(x - 1)}{1}

Step 4: Multiply =(xโˆ’2)(xโˆ’1)=x2โˆ’3x+2= (x - 2)(x - 1) = x^2 - 3x + 2

Answer: x2โˆ’3x+2x^2 - 3x + 2

5Problem 5medium

โ“ Question:

Add: (2x)/(x + 1) + (3)/(x + 1)

๐Ÿ’ก Show Solution

Step 1: Identify that denominators are the same: Both have denominator (x + 1)

Step 2: Add numerators: (2x + 3)/(x + 1)

Step 3: Check if numerator can be factored: 2x + 3 cannot be factored

Step 4: Find restrictions: x โ‰  -1

Answer: (2x + 3)/(x + 1), where x โ‰  -1

6Problem 6medium

โ“ Question:

Subtract: (5)/(2x) - (3)/(4xยฒ)

๐Ÿ’ก Show Solution

Step 1: Find the LCD: Denominators: 2x and 4xยฒ LCD = 4xยฒ

Step 2: Convert to equivalent fractions: (5)/(2x) = (5 ยท 2x)/(2x ยท 2x) = (10x)/(4xยฒ) (3)/(4xยฒ) already has the LCD

Step 3: Subtract numerators: (10x)/(4xยฒ) - (3)/(4xยฒ) = (10x - 3)/(4xยฒ)

Step 4: Check if can be simplified: 10x - 3 cannot be factored with 4xยฒ

Step 5: Find restrictions: x โ‰  0

Answer: (10x - 3)/(4xยฒ), where x โ‰  0

7Problem 7hard

โ“ Question:

Add: 3xโˆ’2+4x+1\frac{3}{x - 2} + \frac{4}{x + 1}

๐Ÿ’ก Show Solution

Step 1: Find LCD LCD=(xโˆ’2)(x+1)\text{LCD} = (x - 2)(x + 1)

Step 2: Rewrite with LCD 3(x+1)(xโˆ’2)(x+1)+4(xโˆ’2)(xโˆ’2)(x+1)\frac{3(x + 1)}{(x - 2)(x + 1)} + \frac{4(x - 2)}{(x - 2)(x + 1)}

Step 3: Add numerators =3(x+1)+4(xโˆ’2)(xโˆ’2)(x+1)= \frac{3(x + 1) + 4(x - 2)}{(x - 2)(x + 1)}

Step 4: Expand and simplify =3x+3+4xโˆ’8(xโˆ’2)(x+1)= \frac{3x + 3 + 4x - 8}{(x - 2)(x + 1)} =7xโˆ’5(xโˆ’2)(x+1)= \frac{7x - 5}{(x - 2)(x + 1)}

Answer: 7xโˆ’5(xโˆ’2)(x+1)\frac{7x - 5}{(x - 2)(x + 1)}

8Problem 8hard

โ“ Question:

Simplify: (x)/(xยฒ - 1) + (2)/(xยฒ + 2x + 1) - (1)/(x + 1)

๐Ÿ’ก Show Solution

Step 1: Factor all denominators: xยฒ - 1 = (x + 1)(x - 1) xยฒ + 2x + 1 = (x + 1)ยฒ x + 1 = (x + 1)

Step 2: Find LCD: LCD = (x + 1)ยฒ(x - 1)

Step 3: Convert each fraction to LCD: x/[(x + 1)(x - 1)] = [x(x + 1)]/[(x + 1)ยฒ(x - 1)]

2/(x + 1)ยฒ = [2(x - 1)]/[(x + 1)ยฒ(x - 1)]

1/(x + 1) = [(x + 1)(x - 1)]/[(x + 1)ยฒ(x - 1)]

Step 4: Combine numerators: [x(x + 1) + 2(x - 1) - (x + 1)(x - 1)]/[(x + 1)ยฒ(x - 1)]

Step 5: Expand numerators: xยฒ + x + 2x - 2 - (xยฒ - 1) = xยฒ + 3x - 2 - xยฒ + 1 = 3x - 1

Step 6: Write final answer: (3x - 1)/[(x + 1)ยฒ(x - 1)]

Step 7: Find restrictions: x โ‰  -1, 1

Answer: (3x - 1)/[(x + 1)ยฒ(x - 1)], where x โ‰  -1, 1