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Aratati ca numarul [tex]a = |2 \sqrt{3} - 5| - \frac{13}{2 \sqrt{3} +5 } } [/tex] este rational

Răspuns :

I2√3-5I=I5-2√3I=5-2√3
13/(2√3+5)=rationalizam=[13(2√3-5)/(12-5)]=(26√3-65)/7
a=5-2√3-(26√3-65)/7=(35-14√3-26√3+65)/7=(100-40√3)/7=20(5-2√3)/7