It is given that the line passes through the point with position vector,
→a=2^i−^j+4^k...(1)
→b=^i+2^j−^k...(2)
It is known that a line through a point with position vector →a and parallel to →b is given by the equation, →r=→a+λ→b
⇒ →r=2^i−^j+4^k+λ(^i+2^j−^k)
This is the required equation of the line in vector form.
⇒x^i−y^j+z^k=(λ+2)^i+(2λ−1)^j+(−λ+4)^k
Eliminating λ, we obtain the Cartesian form equation as
x−21=y+12=z−4−1