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Pe latura AB a patratului ABCD se considera un punct P. Dreptele DP si CP se intersecteaza cu prelungirile laturilor CB si DA in punctele M si, respectiv, N. Daca BM=m si AN=n (m>0,n>0), calculati lungimea laturii patratului ABCD.
Va roooog! E urgent! Raman dator! Dau 30 de puncte!


Răspuns :

[tex]Notam:\\\\ ~x~- ~lungimea ~laturii ~patratului.\\\\ \· NAP\sim\· NDC\Rightarrow \dfrac{n}{x+n}=\dfrac{AP}{x}\Rightarrow AP=\dfrac{nx}{x+n}\\\\ \· MBP\sim\· MCD\Rightarrow \dfrac{m}{x+m}=\dfrac{PB}{x}\Rightarrow PB=\dfrac{mx}{x+m}\\\\ AP+PB=x\Rightarrow\dfrac{nx}{x+n}+\dfrac{mx}{x+m}=x\\\\ \Longleftrightarrow\\\\ n(m+x)+m(x+n)=(x+n)(x+m)\\\\ \Longleftrightarrow\\\\ mn+nx+mx+mn=x^2+nx+mx+mn\\\\ \Longrightarrow x^2=mn ~\Longrightarrow~ \bold{x= \sqrt{mn}} [/tex]