平角(へいかく) へいかく noun straight angle; 180-degree angle academic 1. straight angle; angle of 180 degrees An angle of 180 degrees, formed by two rays pointing in exactly opposite directions so that they make a straight line. 平角(へいかく)は180度(ど)だ。 A straight angle is 180 degrees. 直角(ちょっかく)を二(ふた)つ合(あ)わせると平角(へいかく)になる。🔊 Two right angles together make a straight angle. 一直線(いっちょくせん)に並(なら)んだ二(ふた)つの半直線(はんちょくせん)がつくる角(かく)を平角(へいかく)という。🔊 The angle formed by two rays lying in a straight line is called a straight angle. Composed of 平(へい) (flat, level) + 角(かく) (angle). A mathematics term for an angle of exactly 180 degrees.Related words直角(ちょっかく): right angle — 90 degrees鋭角(えいかく): acute angle — less than 90 degrees鈍角(どんかく): obtuse angle — between 90 and 180 degrees Related Words Related: 直角(ちょっかく) (right angle) Related: 鋭角(えいかく) (acute angle) Related: 鈍角(どんかく) (obtuse angle) general Added 2026.5.18 12:04 · Revised 2026.9.2 13:02 27500/27761_heikaku