$(1)\sqrt{81}$的平方根是__________.

$(2)$若点$M(a\text{-}3\text{,}a\text{+}2)$在$y$轴上，则点$M$的坐标是________.

$(3)$已知方程$\left(a\text{-}2\right)x^{\left|a\right|\text{-}1}\text{+}3y\text{=}1$是关于$x$、$y$的二元一次方程，则$a\text{=}$___________________

$(4)$估计$\dfrac{\sqrt{5}\text{-}1}{2}$与$0\text{.}5$的大小关系是：$\dfrac{\sqrt{5}\text{-}1}{2}$______$0\text{.}5\text{.}($填“$\text{ > }$”、“$\text{=}$”、“$\text{ < }$”$)$

$(5)$已知关于$x$，$y$的二元一次方程组$\left\{\begin{matrix}2x\text{+}3y\text{=}k\text{,}\\ x\text{+}2y\text{=-}1\\\end{matrix}\right.$的解互为相反数，则$k$的值是__________.

$(6)$已知点$P$的坐标为$(2\text{-}m\text{,}3m\text{+}6)$，且点$P$到两坐标轴的距离相等，则$m$的值为__________.