Если 
\frac{c}{d}," alt="\frac{a}{b}>\frac{c}{d}," align="absmiddle" class="latex-formula"> то
0\\\\\frac{ad-bc}{bd}>0\; \; \to \\\\ \left \{ {{ad-bc>0} \atop {bd>0}} \right. \; \; ili\; \; \left \{ {{ad-bc<0} \atop {bd<0,}} \right. \\\\ \left \{ {{ad>bc} \atop {bd>0}} \right. \; \; \left \{ {{ad-bc<0} \atop {bd<0\; nevozmozno,t.k.b>0,d>0}} \right. " alt="\frac{a}{b}-\frac{c}{d}>0\\\\\frac{ad-bc}{bd}>0\; \; \to \\\\ \left \{ {{ad-bc>0} \atop {bd>0}} \right. \; \; ili\; \; \left \{ {{ad-bc<0} \atop {bd<0,}} \right. \\\\ \left \{ {{ad>bc} \atop {bd>0}} \right. \; \; \left \{ {{ad-bc<0} \atop {bd<0\; nevozmozno,t.k.b>0,d>0}} \right. " align="absmiddle" class="latex-formula">
ad>bc