Đáp án:
`c)`
`\sqrt{117,5^2-26,5^2-1440}`
`=\sqrt{(117,5-26,5).(117,5+26,5)-1440}`
`=\sqrt{91.144-1440}`
`=\sqrt{13104-1440}`
`=\sqrt{11664}`
`=108`
`2)`
`\sqrt{9-\sqrt{17}}.\sqrt{9+\sqrt{17}}`
`=\sqrt{(9-\sqrt{17}).(9+\sqrt{17})}`
`=\sqrt{9^2-(\sqrt{17})^2}`
`=\sqrt{81-17}`
`=\sqrt{64}`
`=8`
Vậy `\sqrt{9-\sqrt{17}}.\sqrt{9+\sqrt{17}}=8`