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 Proof of triangle properties https://www.khanacademy.org/math/class-9-tg/x06d55bfa213a79fd:triangles/x06d55bfa213a79fd:properties-of-triangles/v/proofs-concerning-isosceles-triangles-indian-accent 2025-06-04T10:04:13.13703146Z Proofs concerning isosceles triangles Lets proves that the base angles in isosceles triangles are congruent, and conversely, that triangles with congruent base angles are isosceles. He also proves that the perpendicular to the base of an isosceles triangle bisects it. Aakash Bagga video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Proofs concerning isosceles triangles Lets proves that the base angles in isosceles triangles are congruent, and conversely, that triangles with congruent base angles are isosceles. He also proves that the perpendicular to the base of an isosceles triangle bisects it. https://cdn.kastatic.org/ka-youtube-converted/SV5MpEfTYOg.mp4/SV5MpEfTYOg.mp4 543 Proof of triangle properties https://www.khanacademy.org/math/geometry/hs-geo-congruence/hs-geo-congruence-theorems/v/equilateral-triangle-sides-and-angles-congruent 2021-02-16T16:08:14Z Proofs concerning equilateral triangles Sal proves that the angles of an equilateral triangle are all congruent (and therefore they all measure 60°), and conversely, that triangles with all congruent angles are equilateral. Sal Khan video https://cdn.kastatic.org/googleusercontent/QZ8jOQF11Eu-j3PcjFZSdaTq-lwCZ6mvoESc1Nv7ewc_iNlTMDB0BhS4Mzs2690ta8FsShYI4_IxL0-nJN-RywQJ Proofs concerning equilateral triangles Sal proves that the angles of an equilateral triangle are all congruent (and therefore they all measure 60°), and conversely, that triangles with all congruent angles are equilateral. https://cdn.kastatic.org/ka-youtube-converted/CYNUwiUzlPk.mp4/CYNUwiUzlPk.mp4 389 Proof of triangle properties