Implicit Differentiation
Differentiating equations where y is not isolated β treating y as a function of x and applying the chain rule to every term.
Definition
Implicit differentiation finds when is defined implicitly by an equation in and , rather than explicitly as .
The key rule: treat as a function of , and apply the chain rule whenever you differentiate a term involving :
Procedure:
- Differentiate both sides with respect to .
- Apply the chain rule to every term (multiply by ).
- Collect all terms on one side.
- Solve for .
Circle: xΒ² + yΒ² = rΒ²
Differentiate with respect to ( is constant):
At the point on a circle of radius : .
This matches the geometric fact that the tangent to a circle is perpendicular to the radius (slope of radius , perpendicular slope ).
Try it
Find for the ellipse . Find the slope at .
Solution
Differentiate: .
At : . The tangent is horizontal β the ellipse is at its top.
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