Co-interior angles — Grade 8 Math, what it means and where it is taught
Between the parallels, same side. They add to 180°.
Taught in Grade 8 Math.
Where it is taught
Practise this idea
4 questions in the course bank use Co-interior angles, in Geometric Construction, Angle Relationships.
Problem 1
Two parallel lines are cut by a transversal. One angle is 73°. Find the co-interior angle on the same side.
Worked answer
107
180 - 73 = 107°
Problem 2
Two parallel lines are cut by a transversal. One angle is 110°. Find the co-interior angle on the same side.
Worked answer
70
180 - 110 = 70
70°
Problem 3
Co-interior angles measure (3x)° and (2x + 30)°. Find x.
Worked answer
30
3x + 2x + 30 = 180
5x = 150
x = 30
Problem 4
Which pair of angles is not necessarily equal when two parallel lines are cut by a transversal?
- Co-interior angles
- Corresponding angles
- Alternate interior angles
- Vertical angles
Worked answer
Co-interior angles
Co-interior angles are supplementary, not equal
They are only equal in the special case of 90° each