What is the number of possible values of k for which the line joining the points (k, 1, 3) and (1, -2, k + 1) also passes through the point (15, 2, -4)?

The foot of the perpendicular drawn from the origin to the plane x + y + z = 3 is

A vector $\vec r=a \hat i+b \hat j$ is equally inclined to both x and y axes. If the magnitude of the vector is 2 units, then what are the values of a and b respectively?

Consider the following statements in respect of a vector $\vec c=\vec a+\vec b$, where $|\vec a|=|\vec b|\ne0$:

1. $\vec c$ is perpendicular to $(\vec a-\vec b).$

2. $\vec c$ is perpendicular to $\vec a \times \vec b.$

Which of the above statement is/are correct?