Mathematica requires correct syntax, and is case sensitive. It also distinguishes between exact and approximate numbers.
In[1]:= (* it returns the same to represent an exact number *)
Sqrt[3]
Out[1]= Sqrt[3]
In[2]:= (* we can ask for an approximate representation *)
N[Sqrt[3]]
Out[2]= 1.73205
In[3]:= (* or if we give it an approximate number, we get one back *)
\
Sqrt[3.]
Out[3]= 1.73205