[tex]\sqrt{21}[/tex] / [tex]\sqrt{63}[/tex] = [tex]\sqrt{21}[/tex] / 3[tex]\sqrt{7}[/tex] ( amplificam cu [tex]\sqrt{7}[/tex]) = [tex]\sqrt{21}[/tex] * [tex]\sqrt{7}[/tex] / 3 * 7 = [tex]\sqrt{147}[/tex] / 21 = 7[tex]\sqrt{3}[/tex] / 21 ( se imparte 21 la 7 ) = [tex]\sqrt{3}[/tex] / 3