3.
已知长为\(2\)的线段\(A\) \(B\)两端点\(A\)和\(B\)分别在\(x\)轴和\(y\)轴上滑动,线段\(AB\)的中点\(M\)的轨迹为曲线\(C\).
\((\)Ⅰ\()\)求曲线\(C\)的方程;
\((\)Ⅱ\()\)点\(P(x,y)\)是曲线\(C\)上的动点,求\(3x-4y\)的取值范围;
\((\)Ⅲ\()\)已知定点\(Q(0, \dfrac {2}{3})\),探究是否存在定点\(T(0,t)(t\neq \dfrac {2}{3})\)和常数\(λ\)满足:对曲线\(C\)上任意一点\(S\),都有\(|ST|=λ|SQ|\)成立?若存在,求出\(t\)和\(λ\);若不存在,请说明理由.