4.
\((1)\)在复平面内,复数\(z=-2i+1\)对应的点到原点的距离是________.
\((2)\)已知\({{2}^{a}}={{5}^{b}}=\sqrt{10}\)则\(\dfrac{1}{a}+\dfrac{1}{b}=\_\_\_\_\_\_\_\_\).
\((3)\)设函数\(f(x)=g(x)+x^{2}\),曲线\(y=g(x)\)在点\((1,g(1))\)处的切线方程为\(9x+y-1=0\),则曲线\(y=f(x)\)在点\((1,f(1))\)处的切线方程为________.
\((4)\)已知函数\(f(x)=\sin ^{2}x+a\cos x+a\),\(a∈R.\)若对于区间\([0,\dfrac{\pi }{2} ]\)上的任意一个\(x\),都有\(f(x)\leqslant 1\)成立,则\(a\)的取值范围是________.