10/05/07 12:28:39
>>442
1,
∀ε>0, δ = 2ε
|x-4| <δ ⇒ |x^(1/2) -2| = |x-4|/|x^(1/2) +2| ≦ |x-4|/2 < ε
2,
∀ε>0, δ = -3+√(ε+9)
|x-3| < δ ⇒ |(x^2 +1)-10| = |x-3| |x+3| < δ (δ+6) = ε
3,
∀ε>0, δ = 4ε
|x-8| < δ ⇒ | x^(1/3) - 2| = |x-8|/|x^(2/3) + 2x^(1/3) + 4|
< δ/4 = ε