To solve the problem, we need to use the properties of inscribed angles and their corresponding arcs in a circle.
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Understanding the Configuration:
- Triangle XYZ is inscribed in a circle with diameter XZ. By the inscribed angle theorem, any angle inscribed in a circle that subtends a diameter is a right angle. Therefore, angle Y (the angle at vertex Y of triangle XYZ) is a right angle (90°).
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Given Information:
- Angle X = 59°.
- Angle Y = 90° (since it's subtended by the diameter XZ).
- We can find angle Z using the fact that the sum of the angles in a triangle is 180°: \[ Angle Z = 180° - Angle X - Angle Y = 180° - 59° - 90° = 31°. \]
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Finding Arc XY:
- The measure of an arc that subtends an inscribed angle is twice the inscribed angle. Since angle Y subtends arc XY, we have: \[ Arc XY = 2 \times Angle Y = 2 \times 90° = 180°. \]
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Determining the Measure of Arc XY:
- However, we're interested in the arc measure between points X and Y, which is subtended by angle Z at point Y.
- The measure of arc XY corresponds to angle Z: \[ Arc XY = 2 \times Angle Z = 2 \times 31° = 62°. \]
Thus, the arc measure of XY is \( \boxed{62°} \).