This is just called the "sum". Sometimes also the "resultant vector".
resultant
Resultant Vector
No, the sum of two vectors cannot be a scalar.
When the vectors are parallel, i.e. both have the same direction.
This is just called the "sum". Sometimes also the "resultant vector".
I believe the sum of two or more vectors is called a "Resultant."
A resultant Vector.
resultant
Resultant Vector
No, the sum of two vectors cannot be a scalar.
Vectors that sum to zero are coplanar and coplanar vectors sum to zero.
A resultant Vector.
Three vectors sum to zero under the condition that they are coplanar (lie in a common plane) and form a triangle. If the vectors are not coplanar, they will not sum to zero. Another way of looking at it is that the sum is zero if any vector is exactly equal in magnitude and opposite in direction to the vector sum (so-called resultant) of the remaining two.
only if the vectors have the same direction
When the vectors are parallel, i.e. both have the same direction.
Not really. The sum of the magnitudes is a scalar, not a vector - so they can't be equal. But the sum of the two vectors can have the same magnitude, if both vectors point in the same direction.