Trigonometric ratios (English subtitles available)

In preparing for his lessons, a mathematics teacher explains the idea of trigonometry and introduces the application of trigonometric ratios to solve a simple surveying problem. The programme points out that a trigonometric ratio is the ratio of the length of any two sides of a right-angled triangle. The changes of the values of the trigonometric ratios with the sizes of the respective angles are explored with the help of a unit circle on a coordinate plane. The applications of trigonometric ratios in daily life examples are illustrated: angle of inclination of a slope, vertical height of a slope from the ground, area of a farm land.