Given a vector field $\textbf{F}=y^2x \textbf{a}_x-yz \textbf{a}_y-x^2 \textbf{a}_z$ the line integral $\int \textbf{F} \cdot d \textbf{l}$ evaluated along a segment on the $x$-axis from $x=1$ to $x=2$ is

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