1)5-2/3=4+1/3
5-2/3=(15-2)/3=13/3=12/3+1/3=4+1/3
2)√3= (3-√6)(√3+√2)
(3-√6)(√3+√2)
=3√3+3√2-√6*3-√6*2
=3√3+3√2-3√2-2√3
=3√3-2√3+3√2-3√2
=√3
3)√5-2 = [tex]\sqrt{9-4\sqrt{5} }[/tex]
Donc (√5-2)² = [tex](\sqrt{9-4\sqrt{5} })^{2}[/tex]
(√5-2)²
=√5²-2*2√5+2²
=5+4-4√5
=9-4√5
Alors √5-2 = [tex]\sqrt{9-4\sqrt{5} }[/tex]
Et voilà! ;)