\[\boxed{\text{4.\ 383}}\]
\[\textbf{а)}\ \frac{a}{c} = 1\]
\[при\ a = c \neq 0.\]
\[\textbf{б)}\ \frac{a}{c} = 0\]
\[при\ a = 0.\]
\[\textbf{в)}\ \frac{a}{c} = - 1\]
\[при\ a = - c.\]
\[\textbf{г)}\ \frac{c}{a} = 0\]
\[при\ c = 0.\]
\[\textbf{д)}\frac{a}{c} > 0\]
\[при\ a > 0;c > 0\ или\ a < 0;\]
\[c < 0.\]
\[\textbf{е)}\frac{c}{a} < 0\]
\[при\ c > 0;a < 0\ или\ c < 0;\]
\[a > 0.\]
\[\textbf{ж)}\ \frac{a}{c} > 1\]
\[при\ |a| > |c|;\ \ a > 0;c > 0;\]
\[при\ |a| > |c|;\ \ a < 0;\ \ c < 0.\]
\[\textbf{з)}\frac{c}{a} < 1\]
\[при\ |c| < |a|;\ \ a < 0;c > 0;\]
\[при\ |c| < |a|;\ \ a > 0;\ \ c < 0.\]