Calculus

Treating the Derivative of a Product as a Product of Derivatives

Students find the derivative of a product by differentiating each factor and multiplying the results.

Quick check

Why students make it

The rule feels like it should match constant multiples, where the derivative can pass through multiplication by a constant. The mistake is treating two changing factors as if they do not affect each other.

The rule done right

Use the product rule: if y=f(x)g(x)y=f(x)g(x), then y′=f′(x)g(x)+f(x)g′(x)y'=f'(x)g(x)+f(x)g'(x). Keep one factor unchanged while differentiating the other, then add the two terms.