Why does cos(t)=x and sin(t)=y?

Why cos(-x)= cosx?

cos(x)=x

C𝗼𝘀 (-𝘅) = C𝗼𝘀 (𝘅) but WHY ❓

cos(-theta)=cos theta proof | cos minus theta is equal to cos theta

Cos of minus theta is equal to cos theta: proof | Cos(-θ) = Cos(θ) Proof

Derivative of sin(x) and cos(x), PROOF

Derivative of sin(x) : How to find derivative of sin(x) by using First Principle of Derivative! JEE

x^2 + cos x = 2024

Why Cos minus theta is cos theta | Cos(-x) barabar | Cos(-x)=cos x proof | Sin(-x) is equal to |

Verify the Trigonometric Identity cos(pi + x) = -cos(x)

Verify the Trigonometric Identity cos(x - pi/2) = sin(x)

sin(x)+cos(x)=sqrt(2) | Trigonometry

Trigonometric Equation: Solve cos (x) - sin (x) = 0

Prove (1 - sin x)/cos x = cos x / 1 + sin x

Trigonometric Equation: Solve sin (2x) = cos (x)

Proof that the Derivative of cos(x) is -sin(x) using the Limit Definition of the Derivative

Proof that the Derivative of sin(x) is cos(x) using the Limit Definition of the Derivative

Trigonometric equations Solve cos⁡(x)=0.5 Where 0≤x≤2π

Derivatives of sin(x) and cos(x) | Derivative rules | AP Calculus AB | Khan Academy