Đáp án:
`N= -\sqrt{7}-1.`
`P= 3\sqrt{7}+2.`
Giải thích các bước giải:
`N=\sqrt{8-2\sqrt{7}} - \sqrt{28}`
`N=\sqrt{7-2\sqrt{7}+1} - \sqrt{4.7}`
`N=\sqrt{(\sqrt{7})^2-2.\sqrt{7}.1+1^2} - \sqrt{4}.\sqrt{7}`
`N=\sqrt{(\sqrt{7}-1)^2}- 2.\sqrt{7}`
`N=\sqrt{7}-1 - 2.\sqrt{7}` (vì `\sqrt{7}>1`)
`N= -\sqrt{7}-1.`
`P={\sqrt{35}-\sqrt{7}}/{\sqrt{5} - 1} + 12/{\sqrt{7} - 1}`
`P={\sqrt{7}.\sqrt{5}-\sqrt{7}}/{\sqrt{5} - 1} + {12.(\sqrt{7} + 1)}/{(\sqrt{7} - 1)(\sqrt{7} + 1)}`
`P={\sqrt{7}.(\sqrt{5}-1)}/{\sqrt{5} - 1} + {12(\sqrt{7} + 1)}/{(\sqrt{7})^2 - 1^2}`
`P=\sqrt{7}+ {12(\sqrt{7} + 1)}/{7 - 1}`
`P=\sqrt{7}+ {6.2.(\sqrt{7} + 1)}/{6}`
`P=\sqrt{7}+ 2.(\sqrt{7} + 1)`
`P=\sqrt{7}+2\sqrt{7}+2`
`P= 3\sqrt{7}+2.`
