Week 14 – Precalculus 11 – Solving Rational Equations

My Best Mistake of the Week

This week, my best mistake happened when I tried to simplify a mixed-operations rational expression. I understood how to add fractions, but when division and factoring were involved, I forgot the correct order of operations and didn’t factor before simplifying.

The question I made was:

\frac{4x}{2x+4} + \frac{3x}{x^2+5x+6} \div \frac{x}{x+3}

What I Learned

From this mistake, I learned the correct steps for simplifying mixed rational expressions:

  • Rewrite division as multiplication by the reciprocal
  • Factor every polynomial before simplifying
  • Cancel common factors
  • Create a common denominator only when adding
  • Rewrite the final expression properly

Steps That I Did

  1. Rewrite the division as multiplication
    \frac{3x}{x^2+5x+6} \div \frac{x}{x+3} = \frac{3x}{x^2+5x+6} \cdot \frac{x+3}{x}
  2. Factor all expressions
    x^2+5x+6 = (x+2)(x+3)
    2x+4 = 2(x+2)
    So it becomes:
    \frac{3x}{(x+2)(x+3)} \cdot \frac{x+3}{x}
  3. Cancel common factors
    Cancel x and x+3:
    \frac{3}{x+2} \cdot 1 = \frac{3}{x+2}
  4. Substitute this back into the original expression
    Now the whole question becomes:
    \frac{4x}{2x+4} + \frac{3}{x+2}
  5. Factor where possible
    2x+4 = 2(x+2)
    \frac{4x}{2(x+2)} + \frac{3}{x+2} = \frac{2x}{x+2} + \frac{3}{x+2}
  6. Add the fractions
    \frac{2x + 3}{x+2}

Restrictions

x \neq -2,\ 0

Reflection

This mistake helped me understand the importance of factoring first, flipping the second fraction when dividing, canceling carefully, and only adding after rewriting fractions with a common denominator. Once I did that, the expression made sense and became much easier to solve.

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