A math question - a tough one

[Rob]

I am working on a lib part where I need to figure out the point coordinates defined by the distance and vector. See attached image... I am not after the pretty obvious one using cos(a) and sin(a) but a solution based rather on vector translations for a reason that is too long to be explained in this topic, anyway...
X1,Y1 known
X2,Y2 known
D known
X3,Y3 ???

thanks

[TomWaltz]

It's not very clear what you are trying to do... what do you mena by "vector translations"... do you mean ROT2?

[Anonymous]

It's fairly simple if I understand correctly. You can get the distance (let's call it "D1") between the known points and use the proportion.

D1 = SQR((X2-X1)^2 + (Y2-Y1)^2)  ! per Pythagoras

! since (X3-X1)/(X2-X1) = D/D1 then it follows that...

X3 = (D/D1)*(X2-X1) + X1

! and...

Y3 = (D/D1)*(Y2-Y1) + Y1

[Rob]

Matthew, you have nailed it down! that's exactly what I was after...I knew I am very close but I just could not think of that last step... perfect
thanks very much.