The process of finding a derivative is called differentiation. Differentiation and integration constitute the two fundamental operations in single-variable calculus.
The derivative of the sum, diference, product and quotient of:
$$u=u(x)\;\mathrm{and}\;v=v(x)$$
can be found as follows:
\begin{align} {(u\pm v)}'&= {(u)}'\pm {(v)}'\\ \\ {(u\times v)}'&= {u}'\times v + u \times {v}'\\ \\ {\left(\frac{u}{v}\right)}'&= \frac{{u}'\times v - u \times {v}'}{v^{2}}\\ \end{align}
$${(c\times u)}= c \times {u}'$$
$${u\left [ v(x) \right ]}'={u}'\left [ v(x) \right ]\times {v}'(x)$$
What are differentiation rules?
They are formulas for derivatives of sums, products, quotients, constants, and compositions.
Why are they useful?
They make it faster to compute derivatives of common function combinations.