已知三角形的三边按从小到大顺序成等比数列,则公比q的范围是(　　)

A.＜q＜1

B.1＜q＜

C. ＜q＜

D.0＜q＜

若f(x)=2x+3,则f(x+2)的表达式为…(　　)

A.2x+1　　　　　　

B.2x-1

C.2x-3

D.2x+7

试证:对于任意给定的向量a、b都有||a|-|b||≤|a+b|≤|a|+|b|.

已知△ABC中,AB=c,BC=a,AC=b,AB上的中线CD=m,求证:a²+b²=c²+2m².??

已知cos(θ-α)=a,sin(θ-β)=b.?

求证:cos²(α-β)=a²+b²-2absin(α-β).?

已知a、b∈R⁺,求证:≥.?

若a、b、c∈R⁺,求证:≥abc.?

已知a、b、c∈R⁺,求证:(ab+a+b+1)·(ab+ac+bc+c²)≥16abc.?

设f(x)=lg,其中a∈R.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

如果0＜a≤1,求证:当x≠0时,有2f(x)＜f(2x).

已知椭圆=1(a＞b＞0),A、B是椭圆上的两点,线段AB的垂直平分线与x轴交于点P(x₀,0),求证:-.