Negation of the statement $$\forall x \in R, x^2+1=0$$ is

The Cartesian equation of the plane passing through the point A(7, 8, 6) and parallel to the XY plane is

If $$F(\propto)=\left[\begin{array}{ccc}\cos \propto & -\sin \propto & 0 \\ \sin \propto & \cos \propto & 0 \\ 0 & 0 & 1\end{array}\right]$$, where $$\propto \in R$$, then $$[F(\propto)]^{-1}=$$

In a quadrilateral PQRS, M and N are mid-points of the sides PQ and RS respectively. If $$\overline {PS} + \overline {QR} = t\overline {MN} $$, then t =