Multiplying both sides of the above equations by r, we get that x = r cos(θ) and y = r sin(θ).

Question

Revolt · Accepted Answer

By , cos(θ) = , and by , sin(θ) = .:

definition of cosine

By , cos(θ) = , and by , sin(θ) = .:

definition of sine

The states that x2 + y2 = r2.:

Pythagorean theorem

By , we have[r cos(θ)]2 + [r sin(θ)]2 = r2.:

substitution

Applying the , the equation can be written as r2 cos2(θ) + r2 sin2(θ) = r2.:

laws of exponents

Angles and Trigonometric Functions