\(\Rightarrow\int\limits^4_2f\left(t\right)dt=-5\)
Đặt \(2y=t\Rightarrow dy=\frac{1}{2}dt\) ; \(\left\{{}\begin{matrix}y=2\Rightarrow t=4\\y=1\Rightarrow t=2\end{matrix}\right.\)
\(\Rightarrow I=\int\limits^2_4f\left(t\right).\left(\frac{1}{2}dt\right)=-\frac{1}{2}\int\limits^4_2f\left(t\right)dt=\frac{5}{2}\)