题目

已知函数，x∈R. (1)求f(x)的最小正周期和最小值； (2)已知cos(β－α)＝，cos(β＋α)＝－，0＜α＜β≤，求证：[f(β)]2－2＝0. 答案：∴T＝2π，f(x)的最小值为－2. (2)证明：由已知得cos βcos α＋sin βsin α＝，cos βcos α－sin βsin α＝－. 两式相加得2cos βcos α＝0. --- Have you considered _____ your job as a teacher? 　--- Yes. I like the job because a teacher is often considered _____ a gardener. A．to change; to be B．to change; being C．changing; being D．changing; to be