The square root of 51 is approximately 7.1414284285. There is no precise answer because the square root of 51 is an irrational number, meaning the sequence of numbers after the decimal point never ends and never falls into a repeating pattern.
The negative version of this number is also the square root of 51, since multiplying a negative number by itself produces a positive product. Like the positive answer, the negative root is also an irrational number. Irrational numbers, so called because they cannot be expressed as a ratio of two integers, may seem rare or exotic. In fact, all integers that are not perfect squares have irrational square roots.