Differentiation
The rules you must have ready for the exam.
Slope & the rule
3 rulesSlope of a line
m = (y₂-y₁)/(x₂-x₁). y=mx+c → slope m. ax+by+c=0 → m = -a/b.
The rule
y = xⁿ → dy/dx = n xⁿ⁻¹. Multiply by the power, reduce by 1. Constant → 0. dy/dx = slope.
Slope at a point
Differentiate, then substitute the x-value.
Tangents, points & unknowns
2 rulesTangent
Need a point and a slope. Slope from dy/dx; equation y - y₁ = m(x - x₁).
Find a point / unknown
Set dy/dx equal to what you're told and solve. For an unknown letter, sub the known x and slope in.
Turning points & sketching
3 rulesTurning point & nature
dy/dx = 0 for the turning point. d²y/dx² > 0 → min; < 0 → max.
Increasing / decreasing
Increasing where dy/dx > 0; decreasing where dy/dx < 0.
Sketching
Find the roots (y = 0) and the turning point (dy/dx = 0). Mark them and draw the curve.
Motion
1 ruleSpeed & acceleration
v = ds/dt [m/s]; a = d²s/dt² [m/s²]. Initial = t=0; at rest = ds/dt = 0.
Mathslive.ie · Differentiation · Need to Know