$(1)\sqrt{4}+{{(-\dfrac{1}{2})}^{0}}=$ ________.

$(2)$若$a+b=2$，$ab=-1$，则${{a}^{2}}+{{b}^{2}}=$________.
$(3)$如图，已知$\angle AOB=60{}^\circ$，点$C$在边$OA$上，点$D$、$E$在边$OB$上，$CD=CE$，$OC=12$，$DE=2$，则$OD=$________.

$(4)$如图，$D$为$\Delta ABC$内一点，$CD$平分$\angle ACB$，$BD\bot CD$，$\angle A=\angle ABD$，若$AC=\text{8}$，$BC=\text{5}$，则$BD$的长为_______.