Đáp án + Giải thích các bước giải:

 `2sqrt45 + sqrt5 - 3sqrt80`

`= 2*3sqrt5 +sqrt5 - 3*4sqrt5`

` = 6sqrt5 +sqrt5 -12sqrt5`

`= -5sqrt5`

`------`

`sqrt((2-sqrt3)^2) +2/(sqrt3+1) - 6sqrt(16/3)`

`= |2 - sqrt3| + (2(sqrt3-1))/((sqrt3-1)(sqrt3+1)) - 6*4/(sqrt3)`

`= 2-sqrt3 + (2(sqrt3-1))/(3-1) - 8sqrt3`

`=2-sqrt3+ sqrt3 - 1 - 8sqrt3`

`=1-8sqrt3`

`-------`

`tan^2 40^o * sin^2 50^o - 3 + (1-sin40^o)(1+sin40^o)`

`= tan^2 40^o* cos^2 40^o - 3 +  (1 - sin^2 40^o)`

`= (sin^2 40^o)/(cos^2 40^o)* cos^2 40^o - 3 + cos^2 40`

`= sin^2 40^o + cos^2 40^o - 3`

`= 1 -  3 =-2`