Toán Lớp 9: √((√3-√7 )^2 ).√(2/(5-√21))
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Toán Lớp 9: √((√3-√7 )^2 ).√(2/(5-√21))
Nhờ mọi người giải giúp ạ
Comments ( 2 )
=|sqrt{3}-sqrt{7}|.sqrt{(2.(5+sqrt{21}))/((5-sqrt{21})(5+sqrt{21}))}
=(sqrt{7}-sqrt{3}).sqrt{(2.(5+sqrt{21}))/(25-21)} ( |sqrt{3}-sqrt{7}|=sqrt{7}-sqrt{3} vì sqrt{3}<sqrt{7})
=(sqrt{7}-sqrt{3}).sqrt{(2.(5+sqrt{21}))/(4)}
=(sqrt{7}-sqrt{3}).sqrt{(10+2sqrt{21})/4}
=(sqrt{7}-sqrt{3}).sqrt{((sqrt{7})^2+2.sqrt{7}.sqrt{3}+(sqrt{3})^2)/4}
=(sqrt{7}-sqrt{3}).sqrt{((sqrt{7}+sqrt{3})^2)/4}
=(sqrt{7}-sqrt{3}) . sqrt{(sqrt{7}+sqrt{3})^2}/sqrt{4}
=(sqrt{7}-sqrt{3}) . |sqrt{7}+sqrt{3}|/2
=(sqrt{7}-sqrt{3}) . (sqrt{7}+sqrt{3})/2
=((sqrt{7}-sqrt{3})(sqrt{7}+sqrt{3}))/2
=(7-3)/2
=4/2
=2