Derivative Calculator
Calculate the derivative of any cubic polynomial f(x) = ax^3 + bx^2 + cx + d using the power rule, and evaluate it at any point x. The calculator returns both the derivative polynomial f'(x) = 3ax^2 + 2bx + c and its numerical value at your chosen x, which represents the slope of the tangent line at that point.
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Result
Enter values above and click Calculate to see your result.
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Formula
How it works: The power rule states that the derivative of x^n is n times x^(n-1). Applied term by term to a cubic: the derivative of ax^3 is 3ax^2, bx^2 becomes 2bx, cx becomes c, and the constant d becomes 0. The calculator then substitutes your x value into the derivative polynomial to find the slope at that specific point.
Worked Example
Frequently Asked Questions
Why is this limited to cubic (degree 3) polynomials?
This calculator covers polynomials up to degree 3 (ax^3 + bx^2 + cx + d) with a clean interface. For higher-degree polynomials, set unused coefficients to 0. For quadratics, set a = 0. For linear functions, set a = 0 and b = 0.
What does the derivative value at a point mean?
The derivative f'(x) at a specific x gives the instantaneous rate of change, which is the slope of the tangent line to the curve at that point. A positive value means the function is increasing, negative means decreasing, and zero means a potential local maximum or minimum.
Can I use this for exponential or trigonometric functions?
No. This calculator uses the polynomial power rule only. For derivatives of sin, cos, e^x, ln(x), and other functions, use a symbolic calculator or computer algebra system.
Can coefficients be decimals or negative numbers?
Yes. All coefficients accept any real number including decimals and negatives. The power rule applies identically regardless of coefficient sign or magnitude.
How do I find where the derivative equals zero?
Set the derivative polynomial 3ax^2 + 2bx + c = 0 and solve the quadratic. The solutions are critical points where the original function may have local maxima, minima, or inflection points. This calculator evaluates f'(x) at a single point; solving for zeros requires the quadratic formula.
Can I use this Derivative Calculator on my own web page?
You can. Look for the "Embed" button near the top of this calculator. It lets you pick a size, border style, and color palette, then gives you an iframe tag to paste into any webpage. The widget is responsive, loads fast, and costs nothing. More details at calculory.com/services/embed-calculators.
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I can help you understand the derivative calculator formula, interpret your results, and answer follow-up questions.
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