Calculus covers differentiation (finding the gradient/rate of change) and integration (its reverse).
Differentiation rule
If $y=x^n$ then $\dfrac{dy}{dx}=n x^{n-1}$
So $\dfrac{d}{dx}(x^2)=2x$, which equals $6$ when $x=3$. Integration reverses this and finds areas under curves.
Remember
- Differentiate $x^n$ → $nx^{n-1}$.
- Differentiation = gradient; integration = area/reverse.