Question

calculati :$\frac{ \sqrt{21}- \sqrt{3} }{7- \sqrt{7} } * \sqrt{7} =$

Answer 1

(√21-√3)/(√7-1)
=(√21-√3)(√7+1)/(√7-1) (√7+1)=
=(7√3-√21+√21-√3)/(7-1)  =
=(7√3-√3)/6  =
=6√3/6  =
=√3


sau
(√21-√3)/(7-√7)  ×√7=
=(√21-√3)(7+√7)/(7-√7) (7+√7)   ×√7=
=(7√21-7√3+7√3-√21)/(49-7)   ×√7=
=(7√21-√21)/42   ×√7=
=6√21/42   ×√7=
=7√3/7
=√3