`c) \sqrt{x^2 + 2x+1} - x (x > -1)`
` = \sqrt{(x+1)^2} - x`
` = |x+1| - x`
Mà `x > -1` nên `x + 1 >0`
Do đó :
`|x+1| - x = x+1 - x = 1`
Vậy `\sqrt{x^2 + 2x+1} - x = 1 (x >-1)`
``
`d) \sqrt{45. 80}`
` = \sqrt{9 . 5 . 5 . 16}`
` = \sqrt{9} . \sqrt{5} . \sqrt{5} . \sqrt{16}`
` = 3 . 5 . 4`
` = 60`