Root Equations

Grade 8 · algebra · 101 practice problems · read aloud

🔊 Listen to this explanation

🧮 What Are Root Equations?

Root equations contain variables under a square root (√) symbol. Solving them helps us find unknown values when dealing with areas, distances, and other real-world measurements. For example, if you know the area of a square, you can find its side length using a root equation!

📝 Step-by-Step Solving Guide

  1. Isolate the root: Get the square root term by itself on one side
  2. Square both sides: Remove the square root by squaring
  3. Solve the equation: Find the value of the variable
  4. Check your answer: Always verify by plugging back in!

🔍 Worked Examples

Example 1: Simple Root Equation

Solve: √(x + 5) = 3

  1. Root is already isolated: √(x + 5) = 3
  2. Square both sides: (√(x + 5))² = 3² → x + 5 = 9
  3. Solve: x = 9 - 5 = 4
  4. Check: √(4 + 5) = √9 = 3 ✓

Example 2: Root with Coefficient

Solve: 2√(x - 1) = 8

  1. Isolate root: √(x - 1) = 4
  2. Square both sides: x - 1 = 16
  3. Solve: x = 17
  4. Check: 2√(17 - 1) = 2√16 = 2×4 = 8 ✓

🚨 Common Mistakes to Avoid

  • Forgetting to check solutions: Squaring can create "extraneous" solutions that don't work in the original equation
  • Incorrect squaring: Remember (√x)² = x, but √(x²) = |x|
  • Not isolating the root first: Always get the root term alone before squaring

💡 Tips & Tricks

  • Double-check rule: Always verify your answer in the original equation
  • Domain reminder: Expressions under square roots must be ≥ 0
  • Memory aid: "Isolate, Square, Solve, Check" - the root equation mantra!

🎯 Practice Suggestions

  • Start with simple equations like √x = 5
  • Practice isolating roots when they're not alone
  • Create your own problems and solve them
  • Mix with other equation types to build flexibility
  • Use graph paper to keep your work organized

Practice problems

6 of the 101, worked through step by step — try them before opening the answer.

1 ∛(x + 8) = 5

Hint: Think about what operation undoes a cube root. You will need to isolate the variable by performing the inverse operation on both sides of the equation.

Show the answer

Answer: 117

  1. The equation is ∛(x + 8) = 5.
  2. To undo the cube root, cube both sides of the equation: (∛(x + 8))³ = 5³.
  3. This simplifies to x + 8 = 125.
  4. Subtract 8 from both sides: x + 8 - 8 = 125 - 8.
  5. This gives x = 117.
  6. Check: ∛(117 + 8) = ∛125 = 5.

The answer is 117.

2 ∛(x - 9) = 4

Hint: To undo a cube root, think about what operation will isolate x. What number cubed equals 4?

Show the answer

Answer: 73

  1. The equation is ∛(x - 9) = 4.
  2. To remove the cube root, cube both sides: (∛(x - 9))^3 = 4^3.
  3. This simplifies to x - 9 = 64.
  4. Add 9 to both sides: x - 9 + 9 = 64 + 9.
  5. x = 73.
  6. Check: ∛(73 - 9) = ∛64 = 4.

The answer is 73.

3 ∛(x + 10) = 5

Hint: To undo a cube root, think about what operation you can apply to both sides of the equation to isolate x.

Show the answer

Answer: 115

  1. The equation is ∛(x + 10) = 5.
  2. To remove the cube root, cube both sides of the equation: (∛(x + 10))³ = 5³.
  3. This simplifies to x + 10 = 125.
  4. Subtract 10 from both sides: x + 10 - 10 = 125 - 10.
  5. This gives x = 115.
  6. Check: ∛(115 + 10) = ∛125 = 5.

The answer is 115.

4 ∛(x + 15) = 7

Hint: Think about what operation undoes a cube root. You will need to isolate the variable by performing the inverse operation on both sides of the equation.

Show the answer

Answer: 328

  1. The equation is ∛(x + 15) = 7.
  2. To eliminate the cube root, cube both sides of the equation: (∛(x + 15))³ = 7³.
  3. This simplifies to x + 15 = 343.
  4. Subtract 15 from both sides to isolate x: x + 15 - 15 = 343 - 15.
  5. This gives x = 328.
  6. Check by substituting back: ∛(328 + 15) = ∛343 = 7.

The answer is 328.

5 ∛(x - 9) = 4.

Hint: To undo a cube root, cube both sides of the equation. Then solve for x by isolating it.

Show the answer

Answer: 73

  1. Start with the equation ∛(x - 9) = 4.
  2. Cube both sides to eliminate the cube root: (∛(x - 9))³ = 4³.
  3. This simplifies to x - 9 = 64.
  4. Add 9 to both sides: x - 9 + 9 = 64 + 9.
  5. x = 73.

The answer is 73.

6 ∛(x + 15) = 6.

Hint: To undo a cube root, think about what operation will isolate the variable. What number cubed equals 6?

Show the answer

Answer: 201

  1. Start with the equation ∛(x + 15) = 6.
  2. To eliminate the cube root, cube both sides: (∛(x + 15))^3 = 6^3.
  3. This simplifies to x + 15 = 216.
  4. Subtract 15 from both sides: x = 216 - 15.
  5. x = 201.

The answer is 201.

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