2. Differentiation Rules Applier — Theory
This tool is designed for learning: it does not only compute the derivative, it also
shows which differentiation rule is applied and how the expression is split into parts
(such as \(u\) and \(v\) in product/quotient rules).
1) The derivative as a limit
\[
f'(a)=\lim_{h\to 0}\frac{f(a+h)-f(a)}{h}
\]
In practice, we compute derivatives using rules that follow from this definition.
2) Rules used by the calculator
Sum/Difference rule
\[
\frac{d}{dx}(u\pm v)=u'\pm v'
\]
Product rule
\[
(uv)'=u'v+uv'
\]
Quotient rule
\[
\left(\frac{u}{v}\right)'=\frac{u'v-uv'}{v^2}
\]
Chain rule
\[
\frac{d}{dx}f(u)=f'(u)\,u'
\]
Power/exponent rule
\[
(u^n)'=n\,u^{n-1}u'
\qquad (\text{when }n\text{ is constant})
\]
3) How to read the step-by-step output
-
Each step shows the current expression, the rule name, and the resulting derivative expression.
-
For product/quotient (and other two-part rules), the tool explicitly shows:
\(u\) and \(v\) (factors or numerator/denominator).
-
Nested structure is displayed via a Level indicator (outer level 0, deeper parts level 1, etc.).
4) Highlighting \(u\) and \(v\) inside the expression
When the option “Highlight \(u\)/\(v\) inside the expression” is enabled, the calculator visually marks
the exact part of the expression used as \(u\) and \(v\) in the rule applied at that step.
- u: highlighted in one color (blue)
- v: highlighted in another color (purple)
- You can switch between highlighting u, v, both, or off using the controls in the step header.
5) Rule selection and error feedback
The “Force top rule” dropdown is an educational check:
if you select (for example) Product rule but the outer structure is actually a quotient,
the calculator will show an error explaining the mismatch.
6) Rule quiz mode
When Rule quiz mode is enabled, you must choose the correct rule for each step before advancing.
If you choose the wrong rule, you get immediate feedback (correct/incorrect).
7) Input syntax notes
- Implicit multiplication is allowed:
2x, (x+1)(x-1), 2sin(x).
- You may type a wrapper such as
d/dx[(3x^2+1)/cos(x)]; the tool extracts the inside expression.
-
Power-of-function shorthand is supported:
cos^2(2x) is interpreted as \((\cos(2x))^2\).
8) Graph controls
- Drag to pan.
- Mouse wheel / pinch to zoom in/out (large zoom-out is supported).
- Auto fit chooses a view that fits both \(f\) and \(f'\) over the current \(x\)-window.
9) Limitations
-
The symbolic simplification is intentionally light (to keep steps readable).
If you want deeper algebraic simplification, add a dedicated simplifier later.
-
\(\lvert u\rvert\) is not differentiable where \(u=0\). The calculator uses \(\frac{u}{\lvert u\rvert}u'\) away from those points.
-
The plot breaks across discontinuities/asymptotes (non-finite values).