What is d/dx [e^(5x) cos(4x)]?

A. e^(5x)(5cos(4x)-4sin(4x))

Step 1: apply the product rule. Step 2: derivative of e^(5x) is 5e^(5x) and derivative of cos(4x) is -4sin(4x), so answer is e^(5x)(5cos(4x)-4sin(4x)). Step 3: tip: in products, differentiate both factors.

Step 1: product rule लगाइए। Step 2: derivative e^(5x) का 5e^(5x) और cos(4x) का -4sin(4x) है, इसलिए answer e^(5x)(5cos(4x)-4sin(4x))। Step 3: tip: product में दोनों parts को differentiate करें।