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A particle moves along the $x$-axis such that at any time $t \geq 0$ its position is $x(t)$, its velocity is $v(t)$, and its acceleration is $a(t)$.$\newline$What is the average acceleration of the particle on the interval $0 \leq t \leq 8 ?$$\newline$$\frac{x(8)-x(0)}{8}$$\newline$$\frac{a(8)-a(0)}{8}$$\newline$$\frac{1}{8} \int_{0}^{8} a(t) d t$$\newline$$\frac{1}{8} \int_{0}^{8} v(t) d t$