Question

minimum number of unequal vectors whose sum is equal to zero is what? and how?

Answer 1

In general, given two vectors of unequal length, adding them will result in a non-zero vector because in order to have a zero vector sum, the first and second vectors must "cancel out." For example, if you travel left 1 meter, you must travel 1 meter right to return to your initial position.

The minimum is three: three vectors of unequal form a triangle.