10.
已知向量\( \overrightarrow{a}=(2\cos α,\sin ^{2}α), \overrightarrow{b}=(2\sin α,t),α∈(0, \dfrac {π}{2}),t\)为实数.
\((1)\)若\( \overrightarrow{a}- \overrightarrow{b}=( \dfrac {2}{5},0)\),求\(t\)的值;
\((2)\)若\(t=1\),且\( \overrightarrow{a}\cdot \overrightarrow{b}=1\),求\(\tan (2α+ \dfrac {π}{4})\)的值.