Question

The force determined by the vector r=(1,-8,-7) is resolved along three mutually perpendicular directions, one of which is in the direction of the vector a=2i+2j+k. Then the vector component of the force r along vector a is

Answer 1

r•a/|a|

Answer 2

Since we know that,
Projection of r vector along a vector=
(r vector)•(a^)
=(i-8j-7k)•(2/3xi+2/3xj+1/3xk)
=(2/3xi-16/3xj-7/3xk)