7.
\((1)\)点\(P(1,2,3)\)关于\(y\)轴的对称点为\(P_{1}\),\(P\)关于坐标平面\(xOz\)的对称点为\(P_{2}\),则\(|{P}_{1}{P}_{2}|= \) .
\((2)\)已知角\(\alpha \)的终边经过点\(P\left( -x,-6 \right)\),且\(\cos \alpha =\dfrac{4}{5}\),则\(x\)的值为_________.
\((3)\)在平面直角坐标系\(xOy\)中,已知圆\({{x}^{2}}+{{y}^{2}}=5\)上有且仅有三个点到直线\(12x-5y+c=0\)的距离为\(1\),则实数\(c\)的值是 .
\((4)\)当直线\(y=k(x-2)+4\) 和曲线\(y=\sqrt{4-{{x}^{2}}}\) 有公共点时,实数\(k\)的取值范围