How is sine of 90 degree possible

I don't know how can a triangle be formed with two angles each 90 degree. If it is not possible, then how do we calculate sin 90 degree = 1 ?

The_trigonometry_functions

Prove sin(90-A)=cosA.avi

Tan 90 Degrees: Value of tan 90 with Proof, Examples and FAQ - mydomain

What is sin(-90 degrees)?

5.2: Unit Circle - Sine and Cosine Functions - Mathematics LibreTexts

The_trigonometry_functions

3 Ways to Calculate Angles - wikiHow

Trigonometric functions - Wikipedia

Trigonometric Functions