Find dydx\frac{d y}{d x}, if x=acos⁡θ,y=asin⁡θx=a \cos \theta, y=a \sin \theta.

Answer: dydx=−cot⁡θ\frac{d y}{d x} = -\cot \theta

Step-by-step solution

Step 1: Differentiate x with respect to θ

We are given xx as a function of θ\theta. To find dxdθ\frac{dx}{d\theta}, we differentiate acos⁡θa \cos \theta with respect to θ\theta. The derivative of cos⁡θ\cos \theta is −sin⁡θ-\sin \theta, so dxdθ=−asin⁡θ\frac{dx}{d\theta} = -a \sin \theta.

Step 2: Differentiate y with respect to θ

Similarly, we differentiate yy with respect to θ\theta. The derivative of asin⁡θa \sin \theta with respect to θ\theta is acos⁡θa \cos \theta, since the derivative of sin⁡θ\sin \theta is cos⁡θ\cos \theta.

Step 3: Apply the Chain Rule

To find dydx\frac{dy}{dx}, we use the chain rule for parametric equations. This rule states that dydx\frac{dy}{dx} can be found by dividing dydθ\frac{dy}{d\theta} by dxdθ\frac{dx}{d\theta}.

Step 4: Substitute and Simplify

Substitute the expressions for dydθ\frac{dy}{d\theta} and dxdθ\frac{dx}{d\theta} that we found in the previous steps. The aa terms cancel out, and cos⁡θsin⁡θ\frac{\cos \theta}{\sin \theta} simplifies to cot⁡θ\cot \theta, resulting in −cot⁡θ-\cot \theta.

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