Short answers, pulled from the story.
Sumerian astronomers divided circles into 360 degrees to track celestial movements. They studied angle measure and ratios of sides in similar triangles without creating a systematic method for finding unknown lengths.
Hipparchus from Nicaea compiled the first known tables of chords in 140 BC. These tables functioned similarly to modern sine value charts and allowed him to solve complex astronomical problems.
Sine equals the ratio of the side opposite the angle divided by the hypotenuse length. Cosine measures the adjacent leg against the hypotenuse while tangent compares the opposite leg to the adjacent leg.
Nasir al-Din al-Tusi is credited as the creator of trigonometry as a distinct mathematical discipline separate from astronomy. He developed spherical trigonometry into its present form and listed six distinct cases for right-angled triangles within this field.
Bartholomaeus Pitiscus became the first person to use the word trigonometry when publishing his book Trigonometria in 1595. Gemma Frisius described the method of triangulation for the first time, a technique still used today in surveying large geographic areas.