c) `\sqrt{117,5^2-26,5^2-1440}`
`=\sqrt{(117,5-26,5)(117,5+26,5)-1440}`
`=\sqrt{91.144-144.10}`
`=\sqrt{144.(91-10)}`
`=\sqrt{144.81}`
`=\sqrt{144}.\sqrt{81}`
`=12.9`
`=108`
Bài `2`:
a) `\sqrt{125}-4\sqrt{45}+3\sqrt{20}-\sqrt{80}`
`=5\sqrt{5}-12\sqrt{5}+6\sqrt{5}-4\sqrt{5}`
`=-5\sqrt{5}`