The triangle has vertices at (0,0), (a,0), and (0,b).
The point (0,0) is at the origin.
The point (a,0) lies on the x-axis at distance ∣a∣ from the origin.
The point (0,b) lies on the y-axis at distance ∣b∣ from the origin.
This forms a right-angled triangle with the right angle at the origin.
The base of the triangle is ∣a∣ units.
The height of the triangle is ∣b∣ units.
Absolute values are used since a and b can be negative, but distances are always positive.
Area =21×base×height
Area =21×∣a∣×∣b∣
Area =21∣ab∣
Therefore, the area of the triangle is 21∣ab∣ square units.