Two sides of an obtuse triangle measure 12 inches and 14 inches. The longest side measures 14 inches. What is the greatest possible whole-number length of the unknown side?

For an obtuse triangle, the square of the longest side is greater than the sum of the squares of the other two sides. Thus, 14² > 12² + x², so x² < 52 and x < about 7.21. The greatest whole number below that is 7, and it satisfies the triangle inequality, so the unknown side can be 7 inches (choice D).

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