Question

Which number is a rational number?
A. √21
B. √36
C. √50
D. √63

Help please? Will give a medal. :-)

Answer 1

look for one that has a whole number as a square root

Answer 2

a rational number means it can be writen as n/m where n and m are integers, m not equal to 0

Answer 3

$$
\sqrt{21}=\sqrt{3\times 7}=\sqrt 3\sqrt 7\\
\sqrt{36}=\sqrt{6^2}=6\\
\sqrt{50}=\sqrt{5\times 10}=\sqrt 5\sqrt {10}=\sqrt 5\sqrt {2\times 5}=\sqrt 5\sqrt {2}\sqrt{5}=5\times \sqrt 2\\
\sqrt{63}=\sqrt{7\times 9}=3\sqrt 7
$$
All the ones with square roots above, which can not be expressed as an integer or a fraction with integers (i.e numerator and denominators as integers) are NOT rational.