On the packaging for a triangular sail, the edge measurements for the sail are listed as 7ft x 15ft x 17ft without unfurling the sail, you want to determine if the sail forms a right triangle, an acute triangle or an obtuse triangle

The law of cosines can be helpful here. The largest angle (C) will be opposite the longest side (c). That law tells us ...

... c² = a² + b² -2ab·cos(C)

Then

... cos(C) = (a² +b² -c²)/(2ab)

We don't actually need the angle. We only need to know the sign of the cosine.

... cos(C) = (7² +15² -17²)/(2·7·15) = -15/210 . . . . negative sign, so C > 90°

The sail has the shape of an obtuse triangle.

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A triangle solver app on your calculator, phone, tablet, or computer can give you the result easily.

could you provide figure.