Skip to content
MathSolver Pro
  • Open the math solver
  • Ask the AI tutor
  • Find an AP course
  • Create a quiz
  • Open the calculator
  • Graphing Calculator
  • Browse all calculators
  • Read math guides
↑ ↓Enter to open · Esc to close
Solve a problem
Simplifying expressionsAlgebraHigh schoolabout 1:09

Simplify (x^2 - 9)/(x^2 - 8x + 15): animated lesson

A narrated, step-by-step simplifying expressions video lesson with captions. Final answer: (x + 3)/(x - 5), for x ≠ 3, x ≠ 5.

Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.4 MB) · Captions (WebVTT)

Steps on screen

  1. 1. The problem
    Worked example
    x2−9x2−8x+15\frac{{x}^{2}-9}{{x}^{2}-8x+15}
  2. 2. Step by step
    1. x2−9x2−8x+15\frac{x^{2} - 9}{x^{2} - 8x + 15}
      Write as a single fraction
    2. (x−3)(x+3)(x−5)(x−3)\frac{(x - 3)(x + 3)}{(x - 5)(x - 3)}
      Factor the numerator and denominator
    3. x+3x−5\frac{x + 3}{x - 5}
      Cancel the common factor
    4. State the excluded values
  3. 3. The answer
    x+3x−5\frac{x + 3}{x - 5}

    (x^2 - 9)/(x^2 - 8x + 15) = (x + 3)/(x - 5)

  4. 4. Check
    • The simplified form was compared with the original at four test points and agrees.

Transcript

The problem. Here is the problem: (x squared minus 9)/(x squared minus 8x plus 15). Simplify the rational expression in x: factor, cancel common factors and state excluded values.

Step by step. Write as a single fraction. Factor the numerator and denominator. Cancel the common factor. The factor x minus 3 appears in both the numerator and the denominator. Cancelling it does not change the value wherever the original expression is defined. State the excluded values. The original expression is undefined where any denominator (or divisor) is zero: x not equal to 3, x not equal to 5. These restrictions stay even if a factor cancelled.

The answer. So the answer is (x plus 3)/(x minus 5), for x not equal to 3, x not equal to 5. In lowest terms the result is (x plus 3)/(x minus 5). Excluded values: x not equal to 3, x not equal to 5.

Check. The simplified form was compared with the original at four test points and agrees.

About simplifying expressions

Simplify algebraic and rational expressions by collecting like terms and cancelling common factors.

More lessons like this

Simplify (x^2 - 9)/(x^2 - 8x + 15): Step-by-Step Lesson