Answer:
(0, a)
Explanation:
We can start by imagining this rectangle as a square.
(This is written as if it is a square:)
The distance that a square reaches on the x-axis (assuming it has its lower left point at the origin, like this one does) is the same distance that it reaches on the y-axis.
meaning that we will have (length, 0) along the x-axis and (0, length) along the y-axis
so, if we are to treat this as a square, the point (2a, 0) means that our opposite vertex is (0, 2a)
However, because this length is only half of the length that it would be (if it were a square), we must divide our length by 2
2a ÷ 2 = a
So, the coordinates of the top-left vertex of this rectangle:
(0, a)