Answer:
28 square units
Step-by-step explanation:
The formula usually used for the area of a triangle is ...
A = (1/2)bh
where b is the base length and h is the height.
Since the bottom two points lie on the horizontal line y=1, it is convenient to choose the line segment between them as the base. That segment has a length that extends from x=-3 to x=4, so it is 7 units long.
The height is the perpendicular distance from the third point (1, 9) to the base (line y=1). The distance in the x direction is the distance from y=1 to y=9, a distance of 8 units.
Putting these numbers for base length and height into the area formula, we get
A = (1/2)(7 units)(8 units) = 28 square units
