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Answer:
(b) 36 in²
Explanation:
The right triangle at lower right has a vertical leg of 3 and a hypotenuse of 5. Then the horizontal leg is ...
√(5² -3²) = √16 = 4
Then the horizontal diagonal is 4+4 = 8. The vertical diagonal is 6+3 = 9. The area is half the product of the diagonals, so is ...
A = 1/2(d1)(d2) = 1/2(8 in)(9 in) = 36 in²
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You could figure the areas of the triangles separately, but you would come to the same result. This formula is good for a rhombus or a kite (or a square, which is also a rhombus), because the diagonals are perpendicular to each other.