The Power Rule
Bring the exponent down, then drop it by one.
Concept
The workhorse rule
The derivative measures slope at a point. For any power of x, the rule is mechanical: d/dx[x^n] = n·x^(n−1).
Constants multiply straight through, and the derivative of a constant is 0 — a flat line has no slope.
d/dx[a·x^n] = a·n·x^(n−1)