3d, projecting from point to plane, is this correct?

[Guest]

Start line S, End line E, P Q R are on plane.
t*(A(Ex-Sx)+B(Ey-Sy)+C(Ez-Sz))=-A(Sx-Px)-B(Sy-Py)-C(Sz-Pz)
Figuring A, B, C.
A=((Qy-Py)*(Rz-Pz))-((Ry-Py)*(Qz-Pz))
B=-((Qx-Px)*(Rz-Pz))+((Rx-Px)*(Qz-Pz))
C=((Qx-Px)*(Ry-Py))-((Rx-Px)*(Qy-Py))
Is all this math correct for projecting from a start point through an end point to a plane? Can you email maybejosiah@aol.com if you find anything wrong or that could be improved? All as per one might be maybe or might not be maybe, maybe or maybe not, maybe.

[Guest]

https://m.youtube.com/watch?v=rL9UXzZYYo4
Parametric equations:
x=Sx+(Ex-Sx)t
y=Sy+(Ey-Sy)t
z=Sz+(Ez-Sz)t
Equatio of plane:
P=x0,y0,z0
a(x-x0)+b(y-y0)+c(z-z0)=0
This much I know and that source is where I get that equation of plane. All as per one might be maybe or might not be maybe, maybe or maybe not, maybe.