Angles in Triangles
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Grades 7–8 Math · Angle Relationships
Angles in Triangles
Angles in triangles worksheet: eight triangles, to find a missing angle from the angle sum or an exterior angle. Grades 7 and 8, with an answer key.
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Teach it first
Angles in a TriangleA teaching handout to hand out before this sheet: the rule, worked examples and common mistakes.- Pages
- 1
- Last updated
- Time
- About 15 minutes
- Answer key
- Included
- Printing
- Black and white
- Related curriculum
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Use the angle sum of a triangle, exterior angles, and the angles made when a line crosses two parallel lines to find missing angles.
Reviewed by Mr. Daniel Carter, Teacher and Mr. Robert Harrison, Teacher. How we check worksheets
How to use this sheet
- Have the child mark the angles that are equal on the diagram before working anything out.
- Write the relationship as an equation, such as x + 65 = 180, before solving.
- For triangle sides, have the child add the two shorter sides and compare with the longest.
Common mistakes
- Mixing up complementary (90 degrees) and supplementary (180 degrees). Supplementary angles make a straight line.
- Assuming angles are equal because they look equal. Use the relationships, not the look.
- For triangle sides, checking only one pair. The two shorter sides together must be longer than the longest side.
