Question

Un cub are suma lungimilor tuturor muchiilor egala cu 108 cm.Aria D'AC este egala cu ?

Answer 1

Sm=108⇒l=108÷12⇒l=9 cm

in ΔABC:AC²=AB²+BC²

            AC=√9²+9²⇒AC=9√2cm

AD'=AC=D'C

ducem:D'M-inaltime

D'M=l√3÷2=9√2·√3÷2=9√6÷2cm

A=AC·D'M÷2=(9√2·9√6÷2)÷2=(81·2√3÷2)÷2=81√3÷2cm²