Bài 1 ;rút gọn biểu thức sau : a, 3√3 + 4√12 - 5√27 b, ( √45 + √80 - √5) : √5 c, 2√5 + 4√20 - 2√45 c, ( 2√2 - √12 + 3√32).√2

Đáp án:

`a)` `-4sqrt3`

`b)` `6`

`c)` `4sqrt5`

`d)` `28-2sqrt6` 

Giải thích các bước giải:

Bài `1` :

`a)` `3sqrt3+4sqrt12-5sqrt27=3sqrt3+8sqrt3-15sqrt3`

`=(3+8-15)sqrt3=-4sqrt3`

`b)` `(sqrt45+sqrt80-sqrt5):sqrt5`

`=sqrt45/sqrt5+sqrt80/sqrt5-sqrt5/sqrt5`

`=sqrt(45/5)+sqrt(80/5)-sqrt(5/5)`

`=sqrt9+sqrt16-sqrt1=3+4-1=6`

`c)` `2sqrt5+4sqrt20-2sqrt45=2sqrt5+8sqrt5-6sqrt5`

`=(2+8-6)sqrt5`

`=4sqrt5`

`d)` `(2sqrt2-sqrt12+3sqrt32)*sqrt2`

`=(2sqrt2-2sqrt3+12sqrt2)*sqrt2`

`=(14sqrt2-2sqrt3)*sqrt2`

`=14sqrt2*sqrt2-2sqrt3*sqrt2`

`=14*2-2sqrt6=28-2sqrt6`.

Đáp án+Giải thích các bước giải:

` a) 3sqrt3+4sqrt12-5sqrt27`

`=3sqrt3+8sqrt3-15sqrt3`

`=-4sqrt3`

`b)(sqrt45+sqrt80-sqrt5):sqrt5`

`=(3sqrt5+4sqrt5-sqrt5):sqrt5`

`=6sqrt5:sqrt5`

`=6`

`c) 2sqrt5+4sqrt20-2sqrt45`

`=2sqrt5+8sqrt5-6sqrt5`

`=4sqrt5`

`d) (2sqrt2-sqrt12+3sqrt32).sqrt2​`

`=(2sqrt2-2sqrt3+12sqrt2).sqrt2`

`=(14sqrt2-2sqrt3).sqrt2`

`=(14sqrt2.sqrt2)-(2sqrt3.sqrt2)`

`=28-2sqrt6`