A square has two diagonals, and a convex pentagon has five diagonals.  How many diagonals does a convex decagon have?
Question:
A square has two diagonals, and a convex pentagon has five diagonals.  How many diagonals does a convex decagon have?
Answer:
Let's think step by step.

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A square has two diagonals, and a convex pentagon has five diagonals.  How many diagonals does a convex decagon have?
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