All of the following are rational except
a. square root of 2
b. -13
c. 14/15
-
d.81

A. Square root of 2

Step-by-step explanation:

This answer is an EXTENDED decimal that never seems to stop, but eventually it will have to. All the others can be easily written as decimals and\or fractions [also improper fractions].

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for ex: the reciprocal of 3/4 is 4/3. it is the opposite.

reciprocal definition:

a mathematical expression or function so related to another that their product is one; the quantity obtained by dividing the number one by a given quantity.