Exercise 1: Vector or Matrix? — Possible Solution
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(A) AN RGB COLOUR — VECTOR
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An RGB colour is a single ordered list of three numbers (red, green,
blue), with no separate rows-and-columns structure — that's exactly
what a vector is. It's a 3-vector in "colour space," the same way a
3D position is a 3-vector in physical space.

(B) A ROTATION APPLIED TO ANY POINT IN A 2D SCENE — MATRIX
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This isn't a single piece of data to store — it's a *rule* that takes
any input vector and produces a rotated output vector. Something that
transforms vectors, rather than being a vector itself, is a matrix.
The same 2x2 rotation matrix can be applied to every point in the
scene.

(C) A SINGLE DATA POINT WITH FIVE NUMERIC FEATURES — VECTOR
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Five numbers describing one thing (one data point) is an ordered
list, not a transformation rule — a 5-dimensional vector, often
literally called a "feature vector" in machine learning.

(D) A FULL BLACK-AND-WHITE IMAGE OF PIXEL BRIGHTNESS VALUES — MATRIX
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An image has a genuine two-dimensional row/column structure — a
brightness value at row i, column j. That row-and-column arrangement
of numbers is precisely a matrix, not a flat list.

WHY THIS WORKS AS AN ANSWER
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Each classification comes from asking the same question this
chapter's own comparison table asks: is this a single ordered list of
numbers (a vector), or is it either a genuinely two-dimensional grid
of numbers or a rule for transforming other vectors (a matrix) —
rather than guessing from the name alone.