Why does the trigonometric function change at 90 and 270 degrees

Why does the trigonometric function change at 90 and 270 degrees? Like sin to cos, tan to cot : r/JEENEETards

Unit Circle Quadrants, Converting, Solving & Memorizing - Lesson

Could someone explain why pKa stays constant here? (Altius FL 3 C/P Q27) : r/Mcat

The_trigonometry_functions

Trigonal Pyramidal is planar or non planar. Give reason for your answers : r/JEENEETards

Title ko ek alternative mila : r/JEENEETards

Why does the trigonometric function change at 90 and 270 degrees? Like sin to cos, tan to cot : r/JEENEETards

Sin 90 Degrees I Formula and its Derivation I Sample Examples

Cofunction Formulas - GeeksforGeeks