Đáp án:
`\sqrt{(8-sqrt{15})/2}+\sqrt{(8+sqrt{15})/2}=\sqrt{(16-2sqrt(15))/4}+sqrt{(16+2sqrt(15))/4}=\sqrt{(15-2sqrt(15)+1)/4}+\sqrt{(15+2sqrt(15)+1)/4}=sqrt{(sqrt{15}-1)^2/4}+\sqrt{(sqrt(15)+1)^2/4}=(sqrt(15)-1)/2+(sqrt(15)+1)/2=(2sqrt(15))/2=sqrt(15)`