\((1)\)用反证法证明“已知五个正数的和等于\(1\),求证:这五个正数中至少有一个大于或等于\(\dfrac{1}{5} \)”时,首先要假设_______________________.
\((2)\)如图所示,直线\(y=x+1(\)记为\(l_{1})\)与直线\(y=mx+n(\)记为\(l_{2})\)相交于点\(P(a,2)\),则关于\(x\)的不等式\(x+1\geqslant mx+n\)的解集为_______\(.\)
\((3)\)如图,在\(Rt\triangle ABC\)中,\(∠ACB=90^{\circ}\),\(∠ABC=58^{\circ}\),将\(Rt\triangle ABC\)绕点\(C\)旋转到\(Rt\triangle A{{'}}B{{'}}C{{'}}\),使点\(B\)恰好落在\(A{{'}}B{{'}}\)上,\(A{{'}}C\)交\(AB\)于点\(D\),则\(∠ADC\)的度数为_____\(.\)
\((4)\)如图,\(AB/\!/CD\),\(BP\)和\(CP\)分别平分\(∠ABC\)和\(∠DCB\),\(AD\)过点\(P\),且与\(AB\)垂直\(.\)若\(AD=8\),则点\(P\)到\(BC\)的距离是______.
\((5)\)如图,在长方形\(ABCD\)中,\(AB=4\),\(BC=6\),点\(E\)为\(BC\)的中点\(.\)将\(\triangle ABE\)沿\(AE\)折叠,使点\(B\)落在长方形内点\(F\)处,连接\(CF.\)则\(CF\)的长为_______.