I am given the line $l:\langle x,y,z\rangle = \langle1,2,4\rangle + \lambda\langle-1,0,8\rangle, \lambda\in \mathbb{R}$.
I am asked to find the projection (as a vector) of the point, $A\equiv(1,1,1)$ onto the line $l$.
I know the equation for projection of a vector onto another vector, and I can find the projection of a point onto a line that would give me a point as the end result. I do not know how to find the projection of a point onto a line (in that form) that would give me a vector as a result. Is there a formula/series of steps to do this?
Best Answer
We need a point $\;B\;$ on the line s.t. $\;\vec{BA}\perp(-1,0,8)\;$ (why?) . Since any such point $\;B\;$ is of the form $\;(-t+1\,,\,2\,,\,8t+4)\;,\;\;t\in\Bbb R\;$ , we need to solve the equation
$$0=\vec{BA}\cdot(-1,0,8)=(t,-1,-8t-3)\cdot(-1,0,8)=-t-64t-24$$
and then substitute the obtained value of $\;t\;$ back in the expression for $\;B\;$
Cofusing stuff here..................................