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Find the constant term.

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

TOPIC 01

2023 JM01

The odd number of negative factors makes the term negative.

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

01 / Standard#Your turn

Find the constant term.

(2x−1x)6\left(2\sqrt x-\frac1{\sqrt x}\right)^6

Official paper · jm01-2023 · I.6 · PDF 2

Official original and suggested answers ↗ · Suggested answer PDF page 5

Skills and prerequisite lessons
  1. Option A−8-8
  2. Option B88
  3. Option C−160-160
  4. Option D160160
  5. Option E11

Working and explanation

BUILD THE REASONING

Hint 1
Track the exponent when choosing k inverse-root factors.
Hint 2
The exponent must be zero.
Worked solution
  1. Write the general term.

    (6k)26−k(−1)kx3−k\binom6k2^{6-k}(-1)^kx^{3-k}
  2. Choose k=3 and evaluate.

    (63)23(−1)3=−160\binom632^3(-1)^3=-160

C: −160.

Checks and common pitfalls: The odd number of negative factors makes the term negative.

Reasoning checklist · self / teacher assessment
  • Teaching assessment checklist, independently authored. Use the original paper for official marks.
  • Write the general term.
    (6k)26−k(−1)kx3−k\binom6k2^{6-k}(-1)^kx^{3-k}
  • Choose k=3 and evaluate.
    (63)23(−1)3=−160\binom632^3(-1)^3=-160

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

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Curriculum and source notes ↗