There are 11 different Mathematics books on a table. The number of ways that Mary chooses 2 books and  Mike chooses 4 books is

Determine the equation of the circle whose center C (-4, -3) that passes through (2, 1).

The number of ways to select 3 committee members out of 11persons is

The number of arrangements of the letters K, I, N, D in a straight line is

Three-digit even numbers can be made using 5, 6, 7, 8 and 9.  The number of ways in which repetition digit is not allowed is

The point of intersection of zx-plane and the line whose equation is

The directed values of two lines are and respectively. The angle between these lines is

If the Cartesian equation of the line is   then direction vector of the line is

The equation of the plane which is parallel to zx-plane is

If nonzero vectors and are perpendicular, then