acute

In Euclidean geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles are also formed by the intersection of two planes. These are called dihedral angles. Two intersecting curves define also an angle, which is the angle of the tangents at the intersection point. For example, the spherical angle formed by two great circles on a sphere equals the dihedral angle between the planes containing the great circles.

Angles smaller than a right angle (less than 90°) are called acute angles ("acute" meaning "sharp"). An angle equal to 90° or π/2 radians is called a right angle. Two lines that form a right angle are said to be normal, orthogonal, or perpendicular. Angles larger than a right angle and smaller than a straight angle [平角] (between 90° and 180°) are called obtuse angles ("obtuse" meaning "blunt"). An angle equal to 180° or π radians is called a straight angle.

The term normal in mathematics is used in the following broad senses:
1. To denote something upright or perpendicular
2. To denote something that is as it should be. In this sense, normal means good or desirable rather than typical
法线(normal line)指始终垂直于某平面的直线。正态分布(Normal distribution)也叫常态分布或高斯分布(Gaussian distribution)。“学为人师，行为世范”是北京师范大学(Beijing Normal University)的校训，它是启功教授在1996年夏天提出的。法: 标准; 规范。范: 模mú子; 榜样。想当榜样不正直还行？If it's not a right angle, it's an wrong angle.

A reference angle is the acute version of any angle determined by repeatedly subtracting or adding straight angle, to the results as necessary, until the magnitude of the result is an acute angle, a value between 0 and 90°. For example, an angle of 30 degrees has a reference angle of 30 degrees, and an angle of 150 degrees also has a reference angle of 30 degrees (180–150). An angle of 750 degrees has a reference angle of 30 degrees (750–720).

The two acute angles in a right triangle are complementary [互余]. supplementary angle: 补角。The adjective complementary is from Latin complementum, associated with the verb complere, "to fill up". An acute angle is "filled up" by its complement to form a right angle.

An acute triangle (or acute-angled triangle) is a triangle with three acute angles (less than 90°). An obtuse triangle (or obtuse-angled triangle) is a triangle with one obtuse angle (greater than 90°) and two acute angles.

Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short period of time (usually less than 24 hours). To be described as acute toxicity, the adverse effects should occur within 14 days of the administration of the substance. Acute toxicity is distinguished from chronic toxicity, which describes the adverse health effects from repeated exposures, often at lower levels, to a substance over a longer time period (months or years). It is widely considered unethical to use humans as test subjects for acute (or chronic) toxicity research.

The words café and résumé are originally French, and in English we often write those words without the accents. In French, however, the accent marks are not optional. The acute accent is only ever found above an "e", as in "é". Its role is to change the pronunciation of the vowel. 百度翻译有法语发音。咖啡音译的特像，不过café是咖啡馆。

汉语有迟钝，敏锐。acute的近义词有quick和smart。“工作好找吗？” 是个尖锐的问题，serious和severe也是acute的近义词。敏锐可以形容感觉，acute可以修饰sense，被锐物扎了都疼啊。

近义词: astute, discerning, distressing, keen, pointed, pointy, penetrating, perspicacious, piercing, shrewd, sagacious, wise
反义词: blunt, chronic, dull, impassive, obtuse, stupid, stolid

六级/考研单词: geometry, ray, junction, curve, sphere, acute, norm, blunt, mathematics, denote, upright, desire, subtract, necessity, magnitude, triangle, complement, adjective, verb, toxic, adverse, multiple, administer, chronic, heal, seldom, accent, pronounce, discern, distress, keen, penetrate, pierce, shrewd, wise