Question

y=f(x)的定義域?yàn)椋?I>a,b］,設(shè)對(duì)任意x₁、x₂∈［a,b］且x₁≠x₂,記Δ=,則下列結(jié)論中正確的是

①y=f(x)在［a,b］上單調(diào)遞增的充要條件是Δ>0;②y=f(x)在［a,b］上單調(diào)遞減的充要條件是Δ<0;③y=

f(x)在［a,b］上是單調(diào)函數(shù)的充要條件是Δ≠0.

A.①②                                                                   B.②③

C.①③                                                                   D.①②③

Answer 1

解析:③不正確,因當(dāng)Δ≠0時(shí),若Δ>0,有x₁<x₂f(x₁)<f(x₂),若Δ<0,有x₁<x₂?f(x₁)>f(x₂),故當(dāng)Δ≠0時(shí),函數(shù)不單調(diào).

答案:A