Question

Where does the Pythagorean Identity sin2 Θ + cos2 Θ = 1 come from? How does it relate to right triangles?

Answer 1

sin^2 + cos^2 = 1

a^2/c^2 + b^2/c^2 = 1

(a^2 + b^2)/c^2 = 1

c^2/c^2 = 1

1 = 1

Answer 2

another way of doing is by using the formula of equation of a unit circle

for a unit circle r=1 and u can use the method of @AbdullahM by expressing x and y in terms of sine and cosine :)