What is the area of the rhombus? y x , 1 − 4 , − 5 − 4 , − 2 − 1 , − 2 − 7 Explanation A diagonal of a rhombus splits the rhombus into two congruent triangles. Let's look at the shaded triangle. Its base is horizontal, so its base length b can be found by subtracting x -coordinates. = b = − 1 − 5 6 y x , 1 − 4 , − 5 − 4 , − 2 − 1 , − 2 − 7 6 Because the base of the shaded triangle is horizontal, its height h is a vertical distance. The vertical distance can be found by subtracting y -coordinates. = h = − − 1 − 4 3 y x , 1 − 4 , − 5 − 4 , − 2 − 1 , − 2 − 7 3 Thus, the area of the shaded triangle is given below. 1 2 bh = · 1 2 · 6 3 = 9 square units So the area of the rhombus is twice this area. Area of rhombus = = · 2 9 18 square units Answer 18 square units