i is commonly used as the unit vector in the x-dimension (a basically meaningless term without more context). 3-dimensional vectors are often written as:

5i + 2j + 3k.

Since you can assume that 2 is getting multiplied by the unit real vector (equal to 1), you can think of 2+3i as

2r + 3i

but why write the 'r' if we know 2*1 = 2?