HUNTERTUTORING
← AP
Get startedBook tutoring

Common Mistakes

Open PDF

Frequent Errors

1. Using ad+bc instead of ad-bc for det(A) (4.11.B.1). 2. Finding an inverse when det(A)=0 (4.11.B.3). 3. Not verifying AA^-1=I (4.11.A.3). 4. Forgetting identity matrix structure (4.11.A.1). 5. Treating AI as undefined (4.11.A.2). 6. Using signed det for area without |det| when area is requested (4.11.B.2). 7. Arithmetic slips in 2x2 inverse formula (4.11.A.4). 8. Confusing parallel vectors with perpendicular when det=0 (4.11.B.2).

Why These Happen

Students jump to inverse formulas before checking determinant.

How to Fix Them

  • Always compute det(A) first.
  • Verify inverse by multiplication.
  • Use |det| for area questions.

Avoidance Scripts

  • Det first, inverse second.
  • Zero det means no inverse.
  • Multiply back to check I.

Quick Self-Check

  • Did I use ad-bc?
  • Is det(A) nonzero before inverting?
  • Did I verify AA^-1=I?

For your personal study only. Copying, printing, screenshotting, or sharing this material is not permitted and may result in loss of access.

Back to 4.11