1 câu trả lời
a,
A=2x+3x
→5A=10x+15x
=3x5+15x+47x5
≥2√3x5.15x+47.55
≥53
→A≥535
Dấu "=" xảy ra khi : x=5 (Tm)
Vậy min
b,
B=x+1/x
= x/16 +1/x + (15x)/16
>= 2\sqrt{x/16 . 1/x}+(15.4)/16
>= 17/4
Dấu "=" xảy ra khi : x=4 (Tm)
Vậy min B=17/4<=>x=4