8.
下列结论中,正确的有\((\) \()\)
\(①\)不存在实数\(k\),使得方程\(x\ln x- \dfrac {1}{2}x^{2}+k=0\)有两个不等实根;
\(②\)已知\(\triangle ABC\)中,\(a\),\(b\),\(c\)分别为角\(A\),\(B\),\(C\)的对边,且\(a^{2}+b^{2}=2c^{2}\),则角\(C\)的最大值为\( \dfrac {π}{6}\);
\(③\)函数\(y= \dfrac {1}{2}\ln \dfrac {1-\cos x}{1+\cos x}\)与\(y=\ln \tan \dfrac {x}{2}\)是同一函数;
\(④\)在椭圆\( \dfrac {x^{2}}{a^{2}}+ \dfrac {y^{2}}{b^{2}}=1(a > b > 0)\),左右顶点分别为\(A\),\(B\),若\(P\)为椭圆上任意一点\((\)不同于\(A\),\(B)\),则直线\(PA\)与直线\(PB\)斜率之积为定值.