Porisma

Worked solution

Read stationary points from a derivative graph

The derivative graph y=f′(x)y=f^{\prime}(x) is shown. Find the x-coordinates of the stationary points of f(x)f(x) and determine their nature.

Expand diagram

Use the scrollbars or arrow keys to inspect details.

Illustrative upward-opening derivative graph with zeros 0 and 2, positive outside(0,2), negative inside. Vertical scale is illustrative; no exact derivative formula is asserted.
Illustrative upward-opening derivative graph with zeros 0 and 2, positive outside(0,2), negative inside. Vertical scale is illustrative; no exact derivative formula is asserted.
Illustrative upward-opening derivative graph with zeros 0 and 2, positive outside(0,2), negative inside. Vertical scale is illustrative; no exact derivative formula is asserted.

CJC · Lecture · Example 3

Locate the zeros of the derivative

The graph crosses the x-axis at x=0x=0 and x=2x=2. Thus f′(x)=0f^{\prime}(x)=0 at these two inputs. The graph is above the axis before 0, below it between 0 and 2, and above it after 2. No formula or vertical scale for the derivative is supplied.

How did this part go?

Use the signs around zero

Immediately left of 0, at 0 and right of 0, the derivative signs are +,0,−+,0,-. The original function’s tangent rises, is horizontal, then falls. Therefore x=0x=0 is a local maximum of ff, as in the Teacher-filled sign/slope table.

How did this part go?

Use the signs around two

The signs around 2 are −,0,+-,0,+. The original function falls, has a horizontal tangent, then rises, so x=2x=2 is a local minimum. The requested outputs are x-coordinates and natures; y-coordinates of ff cannot be recovered from the given derivative graph alone. Both source tables and the Teacher conclusions are retained.

How did this part go?

Common mistakes

A minimum of the derivative graph is not automatically a minimum of the original function.

Solution notes

Both originals visually compared. Complete source working and distinct Teacher guidance integrated; independently authored domain/precision qualifications are identified. No printed marks or past-paper attribution.

Read the hint