Unit 3 · 9th Grade Mathematics

Linear Expressions
& Equations.

Writing, simplifying, and solving linear expressions and single-variable equations and inequalities.

Start studyingTopic B: Solving Equations & Inequalities

Unit 3 — Lesson Video

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Topic A: Expressions & Properties

Lessons 1–4 · Simplifying, distributing, and writing algebraic expressions.

01–02 — Lessons 1–2

Writing & Simplifying Expressions

  • Variable: a letter representing an unknown quantity.
  • Term: a number, variable, or product (e.g., 3x, −5, 7xy).
  • Like terms: same variable and same exponent — can be combined.
  • Distributive property: a(b + c) = ab + ac.
  • Combining: 4x + 2 + 3x − 7 = 7x − 5
2(3x − 4) + 5x = 6x − 8 + 5x = 11x − 8
Practice — Lessons 1–2
Q1 · Short Answer

Simplify: 5(2x + 3) − 4x. Give the coefficient of x.

Q2 · Multiple Choice

Which are like terms?

03–04 — Lessons 3–4

Writing Equations from Context

  • Translate words to math: 'more than' = add, 'less than' = subtract, 'times' = multiply.
  • 'Is' or 'equals' = the = sign.
  • Define your variable clearly before writing the equation.
  • Check your equation makes sense in context.
'A number increased by 7 is 15' → n + 7 = 15 → n = 8.
Practice — Lessons 3–4
Q3 · Short Answer

'Three times a number decreased by 4 equals 11.' Solve for the number.

Q4 · Multiple Choice

Which equation represents: 'twice a number plus 5 equals 17'?

Topic B: Solving Equations & Inequalities

Lessons 5–10 · Multi-step equations, literal equations, and inequalities.

05–07 — Lessons 5–7

Multi-Step Equations

  • Use inverse operations to isolate the variable.
  • Order of operations in reverse: first undo addition/subtraction, then multiplication/division.
  • Variables on both sides: move all variable terms to one side.
  • Distribute first when there are parentheses.
  • Check: substitute your answer back into the original equation.
3(x − 2) = 2x + 5 → 3x − 6 = 2x + 5 → x = 11. Check: 3(9) = 27 = 22+5 ✓
Practice — Lessons 5–7
Q5 · Short Answer

Solve: 4x − 3 = 2x + 9.

Q6 · Multiple Choice

What is the first step to solve 2(x + 4) = 18?

08–10 — Lessons 8–10

Inequalities & Compound Inequalities

  • Solving: same as equations, BUT flip the inequality when multiplying/dividing by a negative.
  • Graph on a number line: open circle for < or >; closed circle for ≤ or ≥.
  • And (compound): both conditions must be true — solution is the overlap.
  • Or (compound): at least one condition is true — union of both solutions.
−2x + 3 > 7 → −2x > 4 → x < −2 (flip because dividing by −2)
Practice — Lessons 8–10
Q7 · Multiple Choice

When solving −3x > 9, what happens to the inequality sign?

Q8 · Short Answer

Solve: 5x + 2 ≤ 17.