
如图,在四棱锥\(P-ABCD\)中,底面\(ABCD\)是平行四边形,\(∠BCD=135^{\circ}\),侧面\(PAB⊥\)底面\(ABCD\),\(∠BAP=90^{\circ}\),\(AB=AC=PA=2\),\(E\),\(F\)分别为\(BC\),\(AD\)的中点,点\(M\)在线段\(PD\)上.
\((\)Ⅰ\()\)求证:\(EF⊥\)平面\(PAC\);
\((\)Ⅱ\()\)如果直线\(ME\)与平面\(PBC\)所成的角和直线\(ME\)与平面\(ABCD\)所成的角相等,求\( \dfrac {PM}{PD}\)的值.