More Differentiation Rules and Applications
The sine and cosine functions follow special differentiation rules you'll need to memorize: the derivative of sin(x) is cos(x), while the derivative of cos(x) is -sin(x). Notice how these functions are connected—they rotate into each other through differentiation!
Applying these rules together helps solve complex problems. For instance, when finding the derivative of f(x) = x³ + x² - 2, you simply apply the power rule to each term and get f'(x) = 3x² + 2x. For f(x) = 3x³ - 2x² + 1/x, the derivative becomes f'(x) = 9x² - 4x - 1/x².
Horizontal tangent lines occur when a function's derivative equals zero. These points often represent peaks, valleys, or inflection points on graphs. To find them, take the derivative of your function, set it equal to zero, and solve for x.
Remember: Horizontal tangent lines indicate where a function momentarily stops increasing or decreasing—like reaching the top of a hill before going down.
For example, the function f(x) = 3x² - 2x + 1 has a horizontal tangent line at x = 1/3 because f'(x) = 6x - 2 equals zero at that point. For trigonometric functions like f(x) = -cos(x), horizontal tangent lines occur at x = 0, π, 2π, and so on.