Q1
An exterior angle of a triangle equals the sum of:
Athe two opposite interior angles
Ball three interior angles
Conly one interior angle
Dthe adjacent interior angle only
CBSEClass 7 (CBSE)MathematicsCh 7 · Topic 2
Exterior Angle of a Triangle
Learning the relationship between a triangle's exterior angle and its interior angles.
Core concept
This theorem provides a useful shortcut: instead of needing to know all three interior angles to find an unknown angle, only two are needed if the exterior angle relationship is used correctly. This property is derived directly from the fact that the interior angle sum is 180° and that the interior and exterior angle at any single vertex are supplementary (add up to 180°), making the Exterior Angle Theorem a logical consequence rather than an entirely separate, unrelated rule.
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• Exterior Angle Theorem: an exterior angle equals the sum of the two non-adjacent (opposite) interior angles.
• This theorem is a useful shortcut for finding unknown angles without needing all three interior angles.
• It is derived from the triangle angle sum (180°) and interior-exterior angle supplementary relationship.
• An interior and its adjacent exterior angle at the same vertex always add up to 180°.