Assuming you mean:
F1 = 3i - 4j + 2k,
F2 = 2i + 3j - k,
F3 = 2i + 4j - 5k.
Simply add all of them algebraically, i.e. add i's to i's, j's to j's etc. - this works in all dimensions.
The resultant force F will be in your case:
F = 7i + 3j - 4k.
if like parallel forces and unlike parallel forces acts on body at same time what is their resultant force and resultant torque
The magnitude of the resultant of two like parallel forces is the sum of the magnitudes of the forces and its direction will be same as the direction of the parallel forces.
The magnitude of the resultant can be anything between 5N and 15N.
If the resultant of all the forces acting on a body is zero, the forces are called balanced forces. 2 types of unbalanced forces are naet force and resultant force.
the head to tail rule
The resultant.
diagonal
I'd call it the resultant, but "net force" is a good name too.
A resultant force
triangulation method
no
The result is called the Resultant.