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The square root of x is rational if and only if x is a rational number that can be represented as a ratio of two perfect squares. (See square root of 2 for proofs that this is an irrational number, and quadratic irrational for a proof for all non-square natural numbers.)
The positive square root is also known as the principal square root, and is denoted with a radical sign: = Since the square of every real number is nonnegative, negative numbers do not have real square roots. However, for every negative real number there are two imaginary square roots. For example, the square roots of −25 are 5i and −5i ...
Trigonometric number: Any number that is the sine or cosine of a rational multiple of π. Quadratic surd: A root of a quadratic equation with rational coefficients. Such a number is algebraic and can be expressed as the sum of a rational number and the square root of a rational number.
The square root of 2 was likely the first number proved irrational. [27] The golden ratio is another famous quadratic irrational number. The square roots of all natural numbers that are not perfect squares are irrational and a proof may be found in quadratic irrationals.
Impossibility theorems are usually expressible as negative existential propositions or universal propositions in logic. The irrationality of the square root of 2 is one of the oldest proofs of impossibility. It shows that it is impossible to express the square root of 2 as a ratio of two integers.
The square root of 2 is an algebraic number equal to the length of the hypotenuse of a right triangle with legs of length 1. An algebraic number is a number that is a root of a non-zero polynomial in one variable with integer (or, equivalently, rational ) coefficients.
Methods of computing square roots are algorithms for approximating the non-negative square root of a positive real number. Since all square roots of natural numbers , other than of perfect squares , are irrational , [ 1 ] square roots can usually only be computed to some finite precision: these methods typically construct a series of ...
The rational root theorem implies thus that a rational root of Q must belong to {,}, and thus that the rational roots of P satisfy = + {,,,}. This shows again that any rational root of P is positive, and the only remaining candidates are 2 and 2\3 .