Radical Equations
- Indra B. Kshattry PhD
A Radical Equation is an equation in which the variable appears under a radical sign (usually a square root, but it could be any root, such as a cube root, fourth root and so on).
Steps to Solve Radical Equations:
Isolate the Radical.
Eliminate the Radical.
Solve the Resulting Equation.
Check for Extraneous Solutions.
Examples
Example 1: Square Root Radical Equation
Equation: $$ \sqrt{x + 3} = 5 $$
1. Isolate the radical: $$ \sqrt{x + 3} = 5 $$ (already isolated).
2. Eliminate the radical: Square both sides: $$ (\sqrt{x + 3})^2 = 5^2 $$.
$$ x + 3 = 25 $$
3. Solve for $$ x $$:
$$ x = 25 - 3 = 22 $$
4. Check the solution by substituting $$ x = 22 $$ back into the original equation:
$$ \sqrt{22 + 3} = \sqrt{25} = 5 $$
Since both sides are equal, $$ x = 22 $$ is a valid solution.
Example 2: Radical Equation with Multiple Radicals on Different Sides
Equation
$$ \sqrt{3x + 1} = \sqrt{x + 7} $$
Steps to Solve:
Eliminate the Radicals: Square both sides to remove both radicals:
$$ (\sqrt{3x + 1})^2 = (\sqrt{x + 7})^2 $$
$$ 3x + 1 = x + 7 $$
Solve the Resulting Equation: Solve for \(x\):
$$ 2x = 6 $$
$$ x = 3 $$
Check for Extraneous Solutions: Substitute \(x = 3\) back into the original equation to verify it is a valid solution.
Example 3: Cube Root Radical Equation
Equation: $$ \sqrt[3]{2x - 1} = 3 $$
1. Isolate the radical: $$ \sqrt[3]{2x - 1} = 3 $$ (already isolated).
2. Eliminate the radical: Cube both sides: $$ (\sqrt[3]{2x - 1})^3 = 3^3 $$.
$$ 2x - 1 = 27 $$
3. Solve for $$ x $$:
$$ 2x = 27 + 1 = 28 $$
$$ x = \frac{28}{2} = 14 $$
4. Check the solution by substituting $$ x = 14 $$ back into the original equation:
$$ \sqrt[3]{2(14) - 1} = \sqrt[3]{28 - 1} = \sqrt[3]{27} = 3 $$
Since both sides are equal, $$ x = 14 $$ is a valid solution.
Example 4: Radical Equation with a Radical on One Side and an Algebraic Expression on the Other Side
Equation
$$ \sqrt{2x + 7} = 3x - 5 $$
Steps to Solve:
Isolate the Radical: The radical is already isolated on one side.
Eliminate the Radical: Square both sides to remove the square root:
$$ (\sqrt{2x + 7})^2 = (3x - 5)^2 $$
$$ 2x + 7 = 9x^2 - 30x + 25 $$
Solve the Resulting Quadratic Equation: Bring all terms to one side to form a quadratic equation:
$$ 0 = 9x^2 - 32x + 18 $$
Check for Extraneous Solutions: Solve the quadratic equation and check the roots in the original equation to ensure they are valid solutions.
Example 5 : Radical Equation with Two Term Radicals on One Side and an Algebraic Expression on the Other Side
Equation
$$ \sqrt{x + 3} + \sqrt{x - 2} = 4 $$
Steps to Solve:
Isolate One of the Radicals: Move one radical to the other side:
$$ \sqrt{x + 3} = 4 - \sqrt{x - 2} $$
Eliminate the Radical: Square both sides to remove the first radical:
$$ (\sqrt{x + 3})^2 = (4 - \sqrt{x - 2})^2 $$
$$ x + 3 = 16 - 8\sqrt{x - 2} + (x - 2) $$
Isolate the Remaining Radical: Combine like terms and isolate the radical:
$$ 8\sqrt{x - 2} = 21 - 2x $$
Eliminate the Radical Again: Square both sides again to eliminate the second radical:
$$ 64(x - 2) = (21 - 2x)^2 $$
Solve the Resulting Equation: Simplify and solve the resulting equation. Finally, check the solutions to ensure they are valid.
Example 6: Radical Equation with a Quadratic Inside the Radical on One Side and an Algebraic Expression on the Other Side
Equation
$$ \sqrt{x^2 + 4x + 4} = x + 6 $$
Steps to Solve:
Isolate the Radical: The radical is already isolated on one side.
Eliminate the Radical: Square both sides to remove the square root:
$$ (\sqrt{x^2 + 4x + 4})^2 = (x + 6)^2 $$
$$ x^2 + 4x + 4 = x^2 + 12x + 36 $$
Solve the Resulting Equation: Simplify and solve the linear equation:
$$ 4x + 4 = 12x + 36 $$
$$ -8x = 32 $$
$$ x = -4 $$
Check for Extraneous Solutions: Substitute \(x = -4\) back into the original equation to verify it is a valid solution.
Example 7: Radical Equation Involving Higher Powers and More Complex Expressions
Equation
$$ \sqrt[3]{2x^2 - 3x + 7} = x + 2 $$
Steps to Solve:
Isolate the Radical: The radical is already isolated on one side.
Eliminate the Radical: Cube both sides to remove the cube root:
$$ (\sqrt[3]{2x^2 - 3x + 7})^3 = (x + 2)^3 $$
$$ 2x^2 - 3x + 7 = x^3 + 6x^2 + 12x + 8 $$
Solve the Resulting Equation: Rearrange the terms to form a cubic equation:
$$ x^3 + 4x^2 + 15x + 1 = 0 $$
Solve the Cubic Equation: Use methods such as factoring, synthetic division, or numerical approaches to solve for \(x\).
Check for Extraneous Solutions: Ensure that all solutions satisfy the original equation.
Example 8: Radical Equation with a Rational Expression Inside the Radical
Equation
$$ \sqrt{\frac{2x + 3}{x - 1}} = 4 $$
Steps to Solve:
Isolate the Radical: The radical is already isolated on one side.
Eliminate the Radical: Square both sides to remove the square root:
$$ \frac{2x + 3}{x - 1} = 16 $$
Solve the Resulting Rational Equation: Multiply both sides by \(x - 1\):
$$ 2x + 3 = 16(x - 1) $$
$$ 2x + 3 = 16x - 16 $$
Simplify and Solve for \(x\):
$$ 14x = 19 $$
$$ x = \frac{19}{14} $$
Check for Extraneous Solutions: Ensure the solution is valid by substituting it back into the original equation.
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