**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.