WGU Math for Educators D128 Exam Questions and Verified Answers 2026/27 Graded A+
Sum of a polygon - (n-2)180
Right angle - 90 degrees
acute angle - less than 90 degrees
obtuse angle - greater than 90 degrees and less than 180 degrees
reflex angle - greater than 180 degrees
complementary angles - Two angles whose sum is 90 degrees
supplementary angles - Two angles whose sum is 180 degrees
interior angles of a polygon - angles inside of a polygon
triangle - A polygon with three sides whose interior angles equal 180.
isosceles triangle - A triangle that has 2 equal sides.
, equilateral triangle - a triangle with 3 equal sides (60 degrees)
Triangle Inequality Theorem - The sum of the lengths of any two sides of a triangle must
be greater than the length of the third side
scalene triangle - no equal sides
quadrilateral - a four-sided polygon with interior angles adding to 360 degrees
Parallelogram - A quadrilateral with two pairs of parallel sides
square - A quadrilateral with 4 sides that are equal and has all 90 degree angles
rectangle - a parallelogram with 4 right angles
Rhombus - A parallelogram with four congruent sides.
Trapezoid - A quadrilateral with exactly one pair of parallel sides
isosceles trapezoid - a trapezoid whose nonparallel opposite sides are congruent
Sum of a polygon - (n-2)180
Right angle - 90 degrees
acute angle - less than 90 degrees
obtuse angle - greater than 90 degrees and less than 180 degrees
reflex angle - greater than 180 degrees
complementary angles - Two angles whose sum is 90 degrees
supplementary angles - Two angles whose sum is 180 degrees
interior angles of a polygon - angles inside of a polygon
triangle - A polygon with three sides whose interior angles equal 180.
isosceles triangle - A triangle that has 2 equal sides.
, equilateral triangle - a triangle with 3 equal sides (60 degrees)
Triangle Inequality Theorem - The sum of the lengths of any two sides of a triangle must
be greater than the length of the third side
scalene triangle - no equal sides
quadrilateral - a four-sided polygon with interior angles adding to 360 degrees
Parallelogram - A quadrilateral with two pairs of parallel sides
square - A quadrilateral with 4 sides that are equal and has all 90 degree angles
rectangle - a parallelogram with 4 right angles
Rhombus - A parallelogram with four congruent sides.
Trapezoid - A quadrilateral with exactly one pair of parallel sides
isosceles trapezoid - a trapezoid whose nonparallel opposite sides are congruent
