The number of ways , 6 children are arranged in a line such that  two particular children of

them are always together, is

If 3-digit numbers are formed, the number of ways without any repetition is

If and , then is

If and , then is

The unit vector in the same direction of   is

The area of triangle with sides   and is equal to

The distance between the point (2, 3, 6) from the origin is

The directed values of two lines are   

The acute angle between these lines is

In a sphere, if the center (0, 0, 0) and radius 3 units, then the point P(2, 1, 2) lies

The coordinates of the points on the line, which is perpendicular to the zx-plane and passes through the point (a, b, c), are of the form