TK:"https://www.google.com.vn/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjF-cL3pJzxAhWbPXAKHTjTAxwQFjABegQIBRAD&url=https%3A%2F%2Fhoidap247.com%2Fcau-hoi%2F996088&usg=AOvVaw3JxumatFPaPIuCWni48U22"
`sqrt{3-2sqrt2}-sqrt{3+2sqrt2}`
`=sqrt{2-2sqrt2+1}-sqrt{2+2sqrt2+1}`
`=sqrt{(sqrt2-1)^2}-sqrt{(sqrt2+1)^2}`
`=sqrt2-1-sqrt2-1=-2`