Trigonometry deals with angles and sides of right-angle triangles. Trigonometric angles are measured in radians or degrees. Common angles include 0°, 30°, 45°, 60°, 80°, 120°, 180°
Trigonometric ratios are derived from right-angled triangle sides. Three primary functions: sine, cosine, and tangent. Trigonometric ratios help find missing angles and sides in triangles
Sin 1 is a trigonometric function for 1° with value 0.01745. Can be expressed in degrees or radians with same value. Based on right triangle with opposite/hypotenuse ratio
Cosine of 0 degrees equals 1. Cosine represents ratio of adjacent side to hypotenuse in right triangles. Can be expressed as 1/1 in fractions or 1.0 in decimals
Right triangle has one 90° angle and is the basis of trigonometry. Hypotenuse is the longest side opposite the 90° angle. Triangle sides are denoted by a, b, c, with c being hypotenuse. Altitude (h) divides triangle into two similar triangles
Earth's circumference is 40,075.017 km around equator and 40,007.863 km through poles. Earth's shape deviates from spherical by only about 0.3%. Eratosthenes's first measurement was 252,000 stadia, with error between -2.4% and +0.8%