A stationary point is a point on a graph where the gradient is zero.
There are three types of stationary points:
Minimum points -- these are found at the bottom of a positive parabola
Maximum points -- these are found at the top of a negative parabola
Points of inflection -- these are found in the middle of a cubic graph.
We can use differentiation (δy/δx) to find stationary points.
Find the y co-ordinate by substituting the x values into the original equation.
A curve has the equation y = x3 – 6x2 – 36x. Find the co-ordinates of any stationary points on the curve.
y = 63 – (6 x 62) – (36 x 6)
= -216
y = (-2)3 – (6 x (-2)2) – (36 x (-2))
= 40
We can use the second differentiation (δ2y/δx2) to classify stationary points.
Find the second differentiation and solve for the given values
- If δ2y/δx2 < 0, the point is a maximum point
- If δ2y/δx2 > 0, the point is a minimum point
- If δ2y/δx2 = 0, the point is a point of inflection