5.
设函数\(f(x)=\ln x- \dfrac {1}{2}ax^{2}+bx(a > 0),f′(1)=0\).
\((1)\)用含\(a\)的式子表示\(b\);
\((2)\)令\(F(x)=f(x)+ \dfrac {1}{2}ax^{2}-bx+ \dfrac {a}{x}(0 < x\leqslant 3)\),其图象上任意一点\(P(x_{0},y_{0})\)处切线的斜率\(k\leqslant \dfrac {1}{2}\)恒成立,求实数\(a\)的取值范围;
\((3)\)若\(a=2\),试求\(f(x)\)在区间\([c,c+ \dfrac {1}{2}](c > 0)\)上的最大值.