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Why is 2^0.5 equal to sqrt(2)?

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Furthermore, how/why do powers of non-integers work? For example, why would (-1)^1.5 be -i?

Epic8009  Nov 10, 2017
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8+0 Answers

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(-1) ^ 1.5 is 1.

2^0.5 is basically just multiplying 2 0.5 times, which is square root.

supermanaccz  Nov 10, 2017
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I'm not sure I understand. 2*0.5 is NOT sqrt(2).

Epic8009  Nov 10, 2017
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2^0.5   IS   sqrt(2)

Melody  Nov 11, 2017
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(-1)^1.5

$$(-1)^{1.5}\\ = (-1)^{\frac{3}{2}}\\ \text{I can look at this in 2 different ways so lets see what happens.}\\ = [(-1)^3]^{\frac{1}{2}}\qquad or \qquad [(-1)^\frac{1}{2}]^{3}\\ = [-1]^{\frac{1}{2}}\qquad or \qquad [\sqrt{-1}]^{3}\\ =\sqrt{-1}\qquad or \qquad [i]^{3}\\ =\pm i \qquad \qquad or \qquad -i\\$$

The only common answer is -i so I guess that is the only correct answer.

Maybe another mathematician would like to comment here......

Melody  Nov 11, 2017
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How did you get from $$\left(-1\right)^{\frac{1}{2}}$$to $$\sqrt{-1}$$?

Epic8009  Nov 11, 2017
edited by Epic8009  Nov 11, 2017
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This is what WolframAlpha says Melody:

Alan  Nov 11, 2017
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$$(-1)^{\frac{1}{2}}\Rightarrow\sqrt{-1}$$  is a law of fractional exponents. In general terms, $$x^{\frac{a}{b}}=\sqrt[b]{x^a}=\left(\sqrt[b]{x}\right)^a$$

Why is this the case? Well, I can attempt to explain it to you.

The law of exponents explains how to handle multiplication of exponents with identical bases.

$$x^3*x^2=x^{3+2}=x^5$$

Let's try another example but with fractional exponents.

$$3^{\frac{1}{2}}*3^{\frac{1}{2}}=3^{\frac{1}{2}+\frac{1}{2}}=3^1=3$$

In this example here, $$3^{\frac{1}{2}}$$ is a number that when multiplied by itself yields 3. That sounds like the definition of the square root, doesn't it? Therefore, $$3^{\frac{1}{2}}=\sqrt{3}$$. One can also expound upon this.

 $$3^{\frac{1}{3}}*3^{\frac{1}{3}}*3^{\frac{1}{3}}=3^{{\frac{1}{3}}+{\frac{1}{3}}+{\frac{1}{3}}}=3^1=3$$ $$3^{\frac{1}{4}}*3^{\frac{1}{4}}*3^{\frac{1}{4}}*3^{\frac{1}{4}}=3^{\frac{1}{4}+\frac{1}{4}+\frac{1}{4}+\frac{1}{4}}=3^1=3$$ $$3^{\frac{1}{5}}*3^{\frac{1}{5}}*3^{\frac{1}{5}}*3^{\frac{1}{5}}*3^{\frac{1}{5}}=3^{\frac{1}{5}+\frac{1}{5}+\frac{1}{5}+\frac{1}{5}+\frac{1}{5}}=3^1=3$$ $$3^{\frac{1}{x}}*3^{\frac{1}{x}}*3^{\frac{1}{x}}*...*3^{\frac{1}{x}}*3^{\frac{1}{x}}=3^{\frac{1}{x}+\frac{1}{x}+\frac{1}{x}+...+\frac{1}{x}+\frac{1}{x}}=3^1=3$$

The pattern continues. $$3^{\frac{1}{3}}$$ is a number that when multiplied by itself 3 times yields 3. This is the definition of the cubic root. Then, as you can see, I made a generalization. $$3^{\frac{1}{x}}$$, when multiplied x times, yields 3.

TheXSquaredFactor  Nov 11, 2017
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Thank you!

Epic8009  Nov 11, 2017

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