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Stiind ca A supra 11 = B supra 3 , calculati 7A-2B supra 3A+5B

Răspuns :

11b=3a⇒b=3a/11;
⇒7a-2b/3a+5b
⇒7a-2·3a/11/3a+5·3a/11
⇒7a-6a/11/3a+15a/11
⇒77a/11-6a/11/33a/11-15a/11
⇒71a/11/18a/11
⇒71a/11·11/18
⇒71a/1·1/18a
⇒71/1·1/18⇒71/18;
A/11=B/3 sunt proportii,deci A=11B/3 
7 inmultit 11B/3-2B=5 inmultit 11B/3=55B/3