1 câu trả lời
A-\dfrac{159}{32}
=\dfrac{5x^2-9x+12}{(x-1)^2}-\dfrac{159}{32}
=\dfrac{160x^2 -288x + 384 - 159x^2 +318x -159}{32(x-1)^2}
=\dfrac{x^2 +30x +225}{32(x-1)^2}
=\dfrac{(x+15)^2}{32(x-1)^2}>=0
=>A>=\dfrac{159}{32}
Dấu "=" xảy ra khi: x=-15
A_{min}=\dfrac{159}{32}<=>x=-15