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WGU D128 Mathematics for Elementary
Educators OA Exam 2026/2027 Test Bank
with Actual Questions and Verified Answers
Question 1
What is the sum of the interior angles of a polygon?
Correct Answer: (n−2) × 180°
Rationale:
1. The formula (n−2) × 180° gives the sum of interior angles for any
polygon with n sides.
2. This works for triangles (3 sides: 180°), quadrilaterals (4 sides: 360°),
and all other polygons.
3. The formula is derived by dividing the polygon into (n−2) triangles.
4. Each triangle contributes 180° to the total sum.
Question 2
What is a right angle?
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Correct Answer: 90 degrees
Rationale:
1. A right angle measures exactly 90 degrees.
2. It is often denoted by a small square in the angle's corner.
3. Right angles are fundamental in geometry, especially in right triangles
and rectangles.
4. Perpendicular lines intersect to form right angles.
Question 3
What is an acute angle?
Correct Answer: Less than 90 degrees
Rationale:
1. Acute angles measure between 0° and 90°.
2. They are smaller than right angles.
3. Examples include 30°, 45°, and 60°.
4. Acute triangles have all three angles acute.
Question 4
What is an obtuse angle?
Correct Answer: Greater than 90 degrees and less than 180 degrees
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Rationale:
1. Obtuse angles measure between 90° and 180°.
2. They are larger than right angles but less than straight angles.
3. Examples include 120°, 135°, and 150°.
4. Obtuse triangles have one obtuse angle.
Question 5
What is a reflex angle?
Correct Answer: Greater than 180 degrees
Rationale:
1. Reflex angles measure between 180° and 360°.
2. They are larger than straight angles (180°).
3. Examples include 270° and 300°.
4. Reflex angles are often measured on the exterior of a polygon.
Question 6
What are complementary angles?
Correct Answer: Two angles whose sum is 90 degrees
Rationale:
1. Complementary angles add up to 90°.
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2. Each angle is the complement of the other.
3. Example: 30° and 60° are complementary.
4. Complementary angles can be adjacent or non-adjacent.
Question 7
What are supplementary angles?
Correct Answer: Two angles whose sum is 180 degrees
Rationale:
1. Supplementary angles add up to 180°.
2. Each angle is the supplement of the other.
3. Example: 110° and 70° are supplementary.
4. Supplementary angles can be adjacent (forming a linear pair) or non-
adjacent.
Question 8
What are interior angles of a polygon?
Correct Answer: Angles inside of a polygon
Rationale:
1. Interior angles are formed inside a polygon at each vertex.
2. They are the angles between adjacent sides.
WGU D128 Mathematics for Elementary
Educators OA Exam 2026/2027 Test Bank
with Actual Questions and Verified Answers
Question 1
What is the sum of the interior angles of a polygon?
Correct Answer: (n−2) × 180°
Rationale:
1. The formula (n−2) × 180° gives the sum of interior angles for any
polygon with n sides.
2. This works for triangles (3 sides: 180°), quadrilaterals (4 sides: 360°),
and all other polygons.
3. The formula is derived by dividing the polygon into (n−2) triangles.
4. Each triangle contributes 180° to the total sum.
Question 2
What is a right angle?
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Correct Answer: 90 degrees
Rationale:
1. A right angle measures exactly 90 degrees.
2. It is often denoted by a small square in the angle's corner.
3. Right angles are fundamental in geometry, especially in right triangles
and rectangles.
4. Perpendicular lines intersect to form right angles.
Question 3
What is an acute angle?
Correct Answer: Less than 90 degrees
Rationale:
1. Acute angles measure between 0° and 90°.
2. They are smaller than right angles.
3. Examples include 30°, 45°, and 60°.
4. Acute triangles have all three angles acute.
Question 4
What is an obtuse angle?
Correct Answer: Greater than 90 degrees and less than 180 degrees
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Rationale:
1. Obtuse angles measure between 90° and 180°.
2. They are larger than right angles but less than straight angles.
3. Examples include 120°, 135°, and 150°.
4. Obtuse triangles have one obtuse angle.
Question 5
What is a reflex angle?
Correct Answer: Greater than 180 degrees
Rationale:
1. Reflex angles measure between 180° and 360°.
2. They are larger than straight angles (180°).
3. Examples include 270° and 300°.
4. Reflex angles are often measured on the exterior of a polygon.
Question 6
What are complementary angles?
Correct Answer: Two angles whose sum is 90 degrees
Rationale:
1. Complementary angles add up to 90°.
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2. Each angle is the complement of the other.
3. Example: 30° and 60° are complementary.
4. Complementary angles can be adjacent or non-adjacent.
Question 7
What are supplementary angles?
Correct Answer: Two angles whose sum is 180 degrees
Rationale:
1. Supplementary angles add up to 180°.
2. Each angle is the supplement of the other.
3. Example: 110° and 70° are supplementary.
4. Supplementary angles can be adjacent (forming a linear pair) or non-
adjacent.
Question 8
What are interior angles of a polygon?
Correct Answer: Angles inside of a polygon
Rationale:
1. Interior angles are formed inside a polygon at each vertex.
2. They are the angles between adjacent sides.
