[tex]\displaystyle\bf\\\textbf{Grinzile orizontale sunt paralele echidistante taiate de 2 secante.}\\\textbf{De la prima grinda de 1 m pana la ultima grinda de 3 m}\\\textbf{lungimea grinzilor creste liniar asa cum cresc termenii}\\\textbf{unei progresii aritmetice.}\\\\G_1=1~m\\G_5=3~m\\\\Ratia ~~r =\frac{G_5-G_1}{5-1}=\frac{3m-1m}{4}=\frac{2~m}{4}=\frac{1~m}{2}=0,\!5~m\\\\AB=1~m+0,\!5~m=\boxed{\bf1,\!5~m}\\\\CD=AB+0,\!5~m=1,\!5~m+0,\!5=\boxed{\bf2~m}\\\\EF=CD+0,\!5~m=2~m+0,\!5=\boxed{\bf2,\!5~m}[/tex]
