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Equations · Equations

Equations with radicals

An equation with radicals is any equation in which the unknown appears under a root. Here you will see the catalogue of forms you may come across: from a lone square root to nested roots or roots of different indices. The underlying technique is always the same —isolate the radical and raise to the appropriate power— but each form has its own subtleties.

Before you start, make sure you know: Special products (2nd ESO)
Before you start, make sure you know: Quadratic equations (4th ESO)

Isolating and squaring

Flowchart of the solving method: isolating the root, squaring, solving for the unknown and checking the result in the original equation. √(3x−2) = 4 ( )² 3x − 2 = 16 solve x = 6 check check:√(18−2) = 4 ✓
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Solve the following radical equation and check the validity of the solution obtained: $\sqrt{3x - 2} = 4$

Solve the following radical equation and check the validity of the solution obtained:

$\sqrt{3x - 2} = 4$

Solve
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Determine the value of $x$ satisfying the following irrational equation: $\sqrt{2x + 7} - x = 2$

Determine the value of $x$ satisfying the following irrational equation:

$\sqrt{2x + 7} - x = 2$

Solve

Other indices and radicands with fractions

Flowchart of the method for solving an equation with a cube root: isolate the root, cube both sides, solve for the unknown and check the result in the original equation. ∛(5x−4) = −1 ( )³ 5x − 4 = −1 solve x = 3/5 check check:∛(3−4) = −1 ✓
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Solve the following equation containing a higher-order root: $\sqrt[3]{5x - 4} = -1$

Solve the following equation containing a higher-order root:

$\sqrt[3]{5x - 4} = -1$

Solve
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Find the values of $x$ satisfying the following equation with fractions inside the radicand: $\sqrt{\frac{4x - 1}{3}} = 5$

Find the values of $x$ satisfying the following equation with fractions inside the radicand:

$\sqrt{\frac{4x - 1}{3}} = 5$

Solve

Two radicals in the equation

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Find the solution to the equation by equating both radicals and check the result: $\sqrt{x + 5} = \sqrt{3x - 1}$

Find the solution to the equation by equating both radicals and check the result:

$\sqrt{x + 5} = \sqrt{3x - 1}$

Solve
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Solve the following irrational equation containing two radicals: $\sqrt{x + 4} - \sqrt{x - 1} = 1$

Solve the following irrational equation containing two radicals:

$\sqrt{x + 4} - \sqrt{x - 1} = 1$

Solve

Nested radicals and radicals of different indices

Solving scheme for an equation with roots of index two, three and six using the substitution with the sixth root. √x − 7·∛x + 12·⁶√x = 0 t = ⁶√x √x = t³, ∛x = t² t³ − 7t² + 12t = 0 common factor t: t(t²−7t+12)=0
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Find the real solutions to the following equation containing a nested radical (a radical inside another): $\sqrt{x + \sqrt{x + 3}} = 3$

Find the real solutions to the following equation containing a nested radical (a radical inside another):

$\sqrt{x + \sqrt{x + 3}} = 3$

Solve
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Solve the following irrational equation with roots of different indices. It will be very helpful to perform the substitution $t = \sqrt[6]{x}$:…

Solve the following irrational equation with roots of different indices. It will be very helpful to perform the substitution $t = \sqrt[6]{x}$:

$\sqrt{x} - 7\sqrt[3]{x} + 12\sqrt[6]{x} = 0$

Solve

Combined: three radicals and absolute value

Algebraic set-up for solving an equation with three square roots, grouping two on the left-hand side and one on the right-hand side. √(x+2) + √(x−3) = √(3x+4) ( )² → 2√((x+2)(x−3)) = x+5 ( )² again → quadratic equation
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Solve the following irrational equation containing three radicals. Take special care when collecting terms after squaring for the first time:…

Solve the following irrational equation containing three radicals. Take special care when collecting terms after squaring for the first time:

$\sqrt{x + 2} + \sqrt{x - 3} = \sqrt{3x + 4}$

Solve
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Solve the following equation, which combines the properties of absolute values with irrational expressions. Carefully consider the cases for the absolute value:…

Solve the following equation, which combines the properties of absolute values with irrational expressions. Carefully consider the cases for the absolute value:

$|\sqrt{3x + 1} - 4| = 2$

Solve

Applications with radicals

Two diagrams of rearranging variables under a radical: making the height the subject in the free-fall formula and the radius in the volume of a cylinder. t = √(2h / 9,8) solve for h known fall time⇒ solve for h r = √(V / πh) solve for r known volume and height⇒ solve for r
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The base radius $r$ of a cylinder of volume $V$ and height $h$ is calculated using the expression $r = \sqrt{\frac{V}{\pi h}}$. If a cylindrical container of height…

The base radius $r$ of a cylinder of volume $V$ and height $h$ is calculated using the expression $r = \sqrt{\frac{V}{\pi h}}$. If a cylindrical container of height $15\text{ cm}$ has a volume of $471\text{ cm}^3$, set up the corresponding equation and find its base radius (use the approximation $\pi \approx 3,14$).

Solve
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Calculate the $x$-coordinate where a point $P(x, 4)$ must be placed relative to point $A(-2, 1)$ so that the Euclidean distance between them is exactly $5$ units. Set up…

Calculate the $x$-coordinate where a point $P(x, 4)$ must be placed relative to point $A(-2, 1)$ so that the Euclidean distance between them is exactly $5$ units. Set up the corresponding radical equation using the distance formula and solve it.

X Y A(−2,1) y = 4 P(x,4) d = 5
Solve
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Special relativity establishes that the relativistic mass $m$ of a moving object is given by the equation $m = \frac{m_0}{\sqrt{1 - \frac{v^2}{c^2}}}$, where $m_0$ is…

Special relativity establishes that the relativistic mass $m$ of a moving object is given by the equation $m = \frac{m_0}{\sqrt{1 - \frac{v^2}{c^2}}}$, where $m_0$ is the rest mass, $v$ is the velocity of the object and $c$ is the speed of light in a vacuum. Rearrange algebraically to find the velocity $v$ in terms of $m$, $m_0$ and $c$. Subsequently, calculate at what fraction of the speed of light $c$ a spacecraft must travel for its relativistic mass to be exactly double its rest mass.

Solve

Summary

See all the exercises in this section