5.
已知\( \overrightarrow{a}=(1-\cos x,2\sin \dfrac {x}{2}), \overrightarrow{b}=(1+\cos x,2\cos \dfrac {x}{2})\)
\((1)\)若\(f(x)=2+\sin x- \dfrac {1}{4}| \overrightarrow{a}- \overrightarrow{b}|^{2}\),求\(f(x)\)的表达式.
\((2)\)若函数\(f(x)\)和函数\(g(x)\)的图象关于原点对称,求\(g(x)\)的解析式.
\((3)\)若\(h(x)=g(x)-λf(x)+1\)在\([- \dfrac {π}{2}, \dfrac {π}{2}]\)上是增函数,求实数\(λ\)的取值范围.