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InequalitiesAlgebraHigh schoolabout 1:18

Solve -9x - 4 < 9x + 7: animated lesson

A narrated, step-by-step inequalities video lesson with captions. Final answer: (-11/18, ∞).

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 (0.5 MB) · Captions (WebVTT)

Steps on screen

  1. 1. The problem
    Worked example
    −9x−4<9x+7-9x-4 < 9x+7
  2. 2. Step by step
    1. x>−1118x > -\frac{11}{18}
      Move everything to one side and isolate the variable
    2. Test one point in each interval (sign chart)
    3. Decide the endpoints
    4. x∈(−1118,∞)x \in (-\frac{11}{18}, \infty)
      Write the solution set
  3. 3. The answer
    (−1118,∞)(-\frac{11}{18}, \infty)

    x ∈ (-11/18, ∞)

  4. 4. Check
    • x = -2: does not satisfy the inequality.
    • x = 1: satisfies the inequality.

Transcript

The problem. Here is the problem: negative 9x minus 4 less than 9x plus 7. Solve the inequality and give the answer in interval notation.

Step by step. Move everything to one side and isolate the variable. Collect terms: negative 18x minus 11 less than 0. Dividing by a negative coefficient reverses the inequality sign. Test one point in each interval (sign chart). (-∞, negative 11 over 18): test x equals negative 2 → sign plus → excluded; (negative 11 over 18, ∞): test x equals 1 → sign minus → included. Decide the endpoints. negative 11 over 18: excluded. Write the solution set.

The answer. So the answer is (negative 11 over 18, ∞). The inequality holds exactly for x in (negative 11 over 18, ∞). Points where the expression is undefined are never included, and endpoints are included only for less than or equal to or greater than or equal to where the expression equals zero.

Check. x equals negative 2: does not satisfy the inequality. x equals 1: satisfies the inequality.

About inequalities

Solve linear and quadratic inequalities and write the answer as an interval.

More lessons like this

Solve -9x - 4 < 9x + 7: Inequalities Step-by-Step Lesson