Question

已知f（x）=x2-kx+3,在x>-2时恒有f(x)>=2k,求k取值范围

Answer 1

x^2-kx+3≥2k即(x+2)k≤x^2+3,

x>-2,x+2>0所以k≤(x^2+3)/(x+2)=(x+2)+1/(x+2),

因为)(x+2)+1/(x+2),≥2,

所以k≤2.