What does it mean by saying that a number to be constructible or non-constructible.
Please, help

Question

What does it mean by saying that a number to be constructible or non-constructible.
Please, help

loser66 · Answer

@freckles

loser66 · Answer

I understand what it is but not know how to interpret it in formal

loser66 · Answer

$\sqrt 2$ is constructible
$\sqrt[3]2$ is non constructible 
......
but I can't give out the reason why or how to know.

loser66 · Answer

On my book, they just describe how to construct a number, not a formal definition.

freckles · Answer

first time seeing these terms...
i have to look up the word(s)

alexandervonhumboldt2 · Answer

probably this? https://en.wikipedia.org/wiki/Constructible_number

alexandervonhumboldt2 · Answer

looks like if the point is constructable  it can be constructed with  unruled straightedge and compass or ` constructible if and only if it can be written using the four basic arithmetic operations and the extraction of square roots but of no higher-order roots. `

loser66 · Answer

Can I say: From a given length, by using compass and straightedge, we can construct a line segment with the length of a required number. Then, the number is called constructible.