Đáp án:
$D.\ I =\dfrac{1}{24}$
Giải thích các bước giải:
$\quad I = \displaystyle\int\limits_2^{\infty}\dfrac{dx}{x^4}$
$\Leftrightarrow I = \lim\limits_{t\to \infty}\displaystyle\int\limits_2^{t}\dfrac{dx}{x^4}$
$\Leftrightarrow I = \lim\limits_{t\to \infty}\left(-\dfrac{1}{3x^3}\Bigg|_2^t\right)$
$\Leftrightarrow I = \lim\limits_{t\to \infty}\left(-\dfrac{1}{3t^3}\right) - \left(-\dfrac{1}{3.2^3}\right)$
$\Leftrightarrow I = \dfrac{1}{24}$
