Questions tagged [radicals]

For questions involving radical of numbers or radical of expressions (i.e. numbers/expressions raised to the power of a fraction).

A radical expression is any mathematical expression containing a radical symbol $~(√~)~$.

Many people mistakenly call this a 'square root' symbol, and many times it is used to determine the square root of a number. However, it can also be used to describe a cube root, a fourth root, or higher.

When the radical symbol is used to denote any root other than a square root, there will be a superscript number in the $'V'$-shaped part of the symbol. For example, $~3\sqrt{8}~$ means to find the cube root of $~8~$. If there is no superscript number, the radical expression is calling for the square root.

The term underneath the radical symbol is called the radicand.

Steps required for Simplifying Radicals:

Step $~1~$: Find the prime factorization of the number inside the radical. Start by dividing the number by the first prime number $~2~$ and continue dividing by $~2~$ until you get a decimal or remainder. Then divide by $~3,~ 5,~ 7,~$ etc. until the only numbers left are prime numbers. Click on the link to see some examples of Prime Factorization. Also factor any variables inside the radical.

Step $~2~$: Determine the index of the radical. The index tells you how many of a kind you need to put together to be able to move that number or variable from inside the radical to outside the radical. For example, if the index is $~2~$ (a square root), then you need two of a kind to move from inside the radical to outside the radical. If the index is $~3~$ (a cube root), then you need three of a kind to move from inside the radical to outside the radical.

Step $~3~$: Move each group of numbers or variables from inside the radical to outside the radical. If there are nor enough numbers or variables to make a group of two, three, or whatever is needed, then leave those numbers or variables inside the radical. Notice that each group of numbers or variables gets written once when they move outside the radical because they are now one group.

Step $~4~$: Simplify the expressions both inside and outside the radical by multiplying. Multiply all numbers and variables inside the radical together. Multiply all numbers and variables outside the radical together.

A closely related tag is the tag.

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Evaluation of $\sqrt{\frac12+\sqrt{\frac14+\sqrt{\frac18+\cdots+\sqrt{\frac{1}{2^n}}}}}$

I was just playing around with a calculator, and came to the conclusion that: $$\sqrt{\frac12+\sqrt{\frac14+\sqrt{\frac18+\cdots+\sqrt{\frac{1}{2^n}}}}} \approx 1.29$$ Now I'm curious. Is it possible to evaluate the exact value of the following?
Adnan
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Show that $\sqrt[3]{2+\frac {10} 9\sqrt 3}+\sqrt[3]{2-\frac {10} 9\sqrt 3}=2$

Find $\displaystyle\sqrt[3]{2+\frac {10} 9\sqrt 3}+\sqrt[3]{2-\frac {10} 9\sqrt 3}$. I found that, by calculator, it is actually $\bf{2}$. Methods to denest something like $\sqrt{a+b\sqrt c}$ seems to be useless here, what should I do?
JSCB
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Finding summation of inverse of square roots.

Problem: Find the integer part of $$\frac{1}{\sqrt{1}} + \frac{1}{\sqrt{2}} +...+\frac{1}{\sqrt{1000000}}$$ How should I go about approaching this question? I have never seen such a question before, where you cannot multiply any conjugate or…
QuIcKmAtHs
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Why is $15-\sqrt{15}-\sqrt{15-\sqrt{15}}-\sqrt{15-\sqrt{15}-\sqrt{15-\sqrt{15}}}$ so close to $5$?

Basically I started with the number $15$. Then I subtracted its square root to get roughly $11.127$. Subtracting the square root of that returned roughly $7.791$, and finally after taking the square root of that, I got roughly $5$. According to…
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Alternating summation and subtraction of square roots

I encountered a problem, to find the integer part of: $$\frac{1}{\sqrt{1} + \sqrt{2}} + \frac{1}{\sqrt{3} + \sqrt{4}} +...+\frac{1}{\sqrt{99} + \sqrt{100}}$$. I multiplied the conjugate of each denominator. Meaning, for $\frac{1}{\sqrt{a} +…
QuIcKmAtHs
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Why we can't have radicals with negative index?

I am a high school student and we just learned about radical and radical notation. Our teacher says index of radical must be integer and greater than 2 by definition. But I can’t understand why we can’t have radical with negative or rational…
adidas junior
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Can't seem to solve a radical equation? Question is : $\sqrt{x+19} + \sqrt{x-2} = 7$

So there is this equation that I've been trying to solve but keep having trouble with. The unit is about solving Radical equations and the question says Solve: $$\sqrt{x+19} + \sqrt{x-2} = 7$$ I don't want the answer blurted, I want to know how…
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What is the principal cubic root of $-8$?

According to my book it should be a real number, and according to WolframAlpha it should be $1+1.73i$ What is the correct answer?
set5
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Rationalizing mixed denominators?

How would I rationalize the following Fraction? $$ \frac {2}{5-\sqrt2+\sqrt3}$$ I have considered the idea of multiplying by the same radicals, but the 5 prevents that.
BillyK
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Prove that you can't write $\sqrt[3]{4}$ like $a+b\sqrt[3]{2}$

Prove that you can't write $\sqrt[3]{4}$ like $a+b\sqrt[3]{2}$, with $a,b \in \Bbb Q$ How I can prove it? I tried elevating to cube but then? $4 = a^3+ 3a^2b \sqrt[3]{2} + 3ab^2\sqrt[3]{4}+ 2b^3$
Sandrin
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Integral part of $\sqrt{2018+\sqrt{2018+\sqrt{...+2018}}}$

I am tasked to find the integral part of $\sqrt{2018+\sqrt{2018+\sqrt{...+2018}}}$, where the number of $2018$ is $2018$. My attempt: I came up with an upper bound, which was $\sqrt{2018+\sqrt{2018+\sqrt{2018+...}}}$, where there were infinite…
QuIcKmAtHs
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If $\sqrt{28x}$ is an integer is $\sqrt{7x}$ always an integer?

If $\sqrt{28x}$ is an integer is $\sqrt{7x}$ an integer? I have a book that says no, but I cannot think of an example of the contrary... Not looking for a full proof here just wanting to see a counterexample or logic showing that the book is…
Padawan
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How to write $1/ \left(1+\sqrt 3+\sqrt 5+\sqrt{15}\right)$ with a rational denominator?

How to write $\frac{1}{1+\sqrt{3}+\sqrt{5}+\sqrt{15}}$ with a rational denominator? There is an included hint: factorize the denimator Edit: There has been some confusion on this question, the first "1" means "1 over 1+√3+√5+√15" Sorry, I can see…
blah
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Solve $\sqrt{a+bx}+\sqrt{b+cx}+\sqrt{c+ax}=\sqrt{b-ax}+\sqrt{c-bx}+\sqrt{a-cx}$

Let $a,b$ and $c$ be real and positive parameters. Solve the equation $$\sqrt{a+bx}+\sqrt{b+cx}+\sqrt{c+ax}=\sqrt{b-ax}+\sqrt{c-bx}+\sqrt{a-cx}$$ What could I do? Should take the square of both sides?
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How many different integer values can $m$ take?

How many different integer values can $m$ take, given that the following expression is an integer? $$\frac{\sqrt{8}+\sqrt{32}}{\sqrt{m}}$$ Well $$\frac{\sqrt{8}+\sqrt{32}}{\sqrt{m}} = \frac{\sqrt{8}+2\sqrt{8}}{\sqrt{m}} =…
user1270647
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