An error occurred while calling the sqrt () function in vi.

An error occurred while calling the sqrt () function in vi. -- Linux general technology-Linux programming and kernel information. The following is a detailed description. When calling the sqrt () function in vi and debugging with gcc, the following message is displayed: undefined reference to 'sqrt ', collect2: id returned 1 exit status. What is the problem? Thank you.

# Include
Main ()
{
Float a, B, c, disc, x1, x2, p, q;
Scanf ("a = % f, B = % f, c = % f", & a, & B, & c );
Disc = B * B-4 * a * c;
P =-B/(2 * );
Q = sqrt (disc)/(2 * );
X1 = p + q; x2 = p-q;
Printf ("\ n \ nx1 = % 5.2f \ nx2 = % 5.2f \ n", x1, x2 );
}

Undefined reference to 'sqrt'
Collect2: id returned 1 exit status