[tex]\displaystyle\it\\parghia~de~gradul~3~este~acea~parghie~in~care~punctul~de~aplicatie~\\al~fortei~active~se~afla~intre~punctul~de~aplicatie~al~\\fortei~rezistente~si~punctul~de~sprijin.\\in~mod~evident,~bratul~fortei~rezistente~este~de~fapt\\lungimea~parghiei.\\principiul~parghiei:\boxed{\it \frac{F}{R}=\frac{b_R}{b_F}}\\------------------------\\F=300N,~b_F=0,3N,~R=100N.\\din~principiul~parghiei \implies b_R=\frac{b_F F}{R}.\\numeric,~b_R=\frac{300\cdot 0,3}{100}=\boxed{0,9m}.[/tex]
