LEARN · EXPLAIN · REVISE

Find the signed scalar projection on the positive x-axis.

Read the idea, work independently, then explain what changed.

高一必修第二册(A版).pdf · 6.3 · PDF 32 / printed page 25

TOPIC 01

Basis theorem and coordinate representation

Build understanding of basis theorem and coordinate representation through definitions, contrasting cases and justified applications.

Connect geometric and algebraic forms of basis theorem and coordinate representation.
Connect representations and justify the steps, including boundary cases.
Explain a solution and apply the idea to a changed situation.

Use one hint at a time. A correction explains what changed, not just the final answer.

01 / Standard#Your turn

\mathbf a=(-3,3)

Skills and prerequisite lessons

Working and explanation

BUILD THE REASONING

Hint 1

Use a nonparallel basis or Cartesian coordinates and solve component equations.

Hint 2

Dot with a unit vector along the target direction.

Worked solution

The requested value is -3.

Checks and common pitfalls: A signed projection may be negative even though a length is nonnegative.

Think first. Reveal a hint when the class is ready.

Teacher preparation and assessment

What must be true before using the main rule for basis theorem and coordinate representation?
Which representation makes this task easier, and why?
Change one assumption. Does the conclusion survive?

Connect geometric and algebraic forms of basis theorem and coordinate representation.
Basis: Two nonparallel vectors represent every plane vector uniquely.
Coordinate tests: Use scalar multiples for parallelism and zero dot product for perpendicular nonzero vectors.
Close with: conditions → representation → reasoning → check.

Expected reasoning: Two nonparallel vectors represent every plane vector uniquely.
Expected reasoning: Use scalar multiples for parallelism and zero dot product for perpendicular nonzero vectors.
Expected correction: Parallel basis candidates do not span the whole plane.