https://www.khanacademy.org/math/class-7-ncf/x063f95a40c290960:a-tale-of-three-intersecting-lines/x063f95a40c290960:properties-of-triangles-part-2/v/worked-example-triangle-angles-intersecting-lines_indian_accent 2025-06-11T12:53:03.642274817Z Worked example: Triangle angles (intersecting lines) Learn how to find unknown angles in triangles and intersecting lines. We use concepts like supplementary angles (angles that add up to 180°), vertical angles (opposite angles made by two crossing lines), and exterior angles (angles outside a triangle). There are lots of ways to think about this problem. Skyloom (Dubbing) video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Worked example: Triangle angles (intersecting lines) Learn how to find unknown angles in triangles and intersecting lines. We use concepts like supplementary angles (angles that add up to 180°), vertical angles (opposite angles made by two crossing lines), and exterior angles (angles outside a triangle). There are lots of ways to think about this problem. https://cdn.kastatic.org/ka-youtube-converted/gcsBX7aFb2k.mp4/gcsBX7aFb2k.mp4 297 Properties of Triangles Part 2 https://www.khanacademy.org/math/revision-mh-math-class-6/x01cb2212e31ce997:week-3/x01cb2212e31ce997:triangles-and-their-properties/v/angles-in-a-triangle-sum-to-180-proof-indian-accent 2025-06-04T10:11:55.11792485Z Angles in a triangle sum to 180° proof The sum of the interior angle measures of a triangle always adds up to 180;. We can draw a line parallel to the base of any triangle through its third vertex. Then we use transversals, vertical angles, and corresponding angles to rearrange those angle measures into a straight line, proving that they must add up to 180. Skyloom (Dubbing) video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Angles in a triangle sum to 180° proof The sum of the interior angle measures of a triangle always adds up to 180;. We can draw a line parallel to the base of any triangle through its third vertex. Then we use transversals, vertical angles, and corresponding angles to rearrange those angle measures into a straight line, proving that they must add up to 180. https://cdn.kastatic.org/ka-youtube-converted/-IR3SJfOjIc.mp4/-IR3SJfOjIc.mp4 247 Properties of Triangles Part 2 https://www.khanacademy.org/math/cc-eighth-grade-math/cc-8th-geometry/cc-8th-triangle-angles/e/triangle_angles_1 2026-03-31T08:44:48.259988263Z Find angles in triangles Find missing angle measures in triangles using the properties of general triangles, isosceles triangles, and equilateral triangles. Tomer Gal exercise https://www.khanacademy.org/math/class-7-ncf/x063f95a40c290960:a-tale-of-three-intersecting-lines/x063f95a40c290960:properties-of-triangles-part-2/v/exterior-angle-property-of-a-triangle 2024-05-28T09:47:20.658952794Z Exterior angle property of a triangle We look at the exterior angle property of the triangle and a quick problem on how to apply it. Devashish Phadnis video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Exterior angle property of a triangle We look at the exterior angle property of the triangle and a quick problem on how to apply it. https://cdn.kastatic.org/ka-youtube-converted/RFKQq6yvRSc.mp4/RFKQq6yvRSc.mp4 263 Properties of Triangles Part 2 https://www.khanacademy.org/math/class-7-ncf/x063f95a40c290960:a-tale-of-three-intersecting-lines/x063f95a40c290960:properties-of-triangles-part-2/e/understand-exterior-angle-property 2026-04-07T23:17:37.123726494Z Understand triangle exterior angle property Let's learn where and how the triangle exterior angle property can be applied. Aanand exercise https://www.khanacademy.org/districts-courses/geometry-scps-pilot-textbook/x398e4b4a0a333d18:triangle-congruence/x398e4b4a0a333d18:angle-relationships-in-triangles/e/exterior-angle-property-problems 2026-04-07T23:36:17.218592739Z Triangle exterior angle property problems Let's use the exterior angle property to find missing angles. Aanand exercise https://www.khanacademy.org/math/cc-eighth-grade-math/cc-8th-geometry/cc-8th-triangle-angles/e/angles_2 2026-03-31T08:44:48.259988263Z Finding angle measures using triangles Use your knowledge about angles to find missing angle measures in various complex situations. David Lai exercise