Đáp án + giải thích các bước giải:
c) `\sqrt{(3+\sqrt{5})/2}=\sqrt{(6+2\sqrt{5})/4}=\sqrt{(5+2\sqrt{5}+1)/4}=\sqrt{(\sqrt{5}+1)^2/4}=|\sqrt{5}+1|/2=(\sqrt{5}+1)/2 `
d)
`\sqrt{(9+\sqrt{17})/2}=\sqrt{(18+2\sqrt{17})/4}=\sqrt{(17+2\sqrt{17}+1)/4}=\sqrt{(\sqrt{17}+1)^2/4}=|\sqrt{17}+1|/2=(\sqrt{17}+1)/2`
e)
`\sqrt{2/(7-\sqrt{13})}=\sqrt{4/(14-2\sqrt{13})}=\sqrt{4/(13-2\sqrt{13}+1)}=\sqrt{4/(\sqrt{13}-1)^2}=2/|\sqrt{13}-1|=2/(\sqrt{13-1})=(2(\sqrt{13}+1))/((\sqrt{13}-1)(\sqrt{13}+1))=(2(\sqrt{13}+1))/(13-1)=(2(\sqrt{13}+1))/12=(\sqrt{13}+1)/6`
h)
`\sqrt{2/(11-\sqrt{21})}=\sqrt{4/(22-2\sqrt{21})}=\sqrt{4/(21-2\sqrt{21}+1)}=\sqrt{4/(\sqrt{21}-1)^2}=2/|\sqrt{21}-1|=2/(\sqrt{21-1})=(2(\sqrt{21}+1))/((\sqrt{21}-1)(\sqrt{21}+1))=(2(\sqrt{21}+1))/(21-1)=(2(\sqrt{21}+1))/20=(\sqrt{21}+1)/10`
