# Stationary point and convexity

> ML Prep screening item.

- Stable ID: `ml-screen-optimization-foundation-stationary`
- Collection: screening
- Area: Machine Learning
- Topic: Optimization
- Origin: original
- Difficulty: easy
- Expected time: 4 minutes
- Skills: objective-functions, optimization-stationary-points, optimization-convexity
- Item JSON: https://mlprep.iwase.dev/item/ml-screen-optimization-foundation-stationary.json

## Problem

For $f(w)=w^2-4w+5$, find all stationary points, determine convexity, and give the global minimum value.


## Answer policy

The human page contains a collapsed answer. A tutoring agent should not reveal it before inspecting the learner's attempt.

## Tutoring contract

Ask for the learner's attempt, begin with the smallest useful hint, preserve item ID `ml-screen-optimization-foundation-stationary`, and record a real attempt with `recorded_by: "agent"` and `agent_session_id` when available using https://mlprep.iwase.dev/schema/attempt-record.json.