Answer
Yes. Dimension is 4
Work Step by Step
Because A has a pivot in each row, its columns span $R^3$ so $Col\ A = R^3$.
Because the equation $Ax=0$ has 4 free variables because A has 7 columns and 3 pivot columns, the dimension of Nul A is 4.
Linear Algebra and Its Applications (5th Edition)
by Lay, David C.; Lay, Steven R.; McDonald, Judi J.
Published by
Pearson
ISBN 10:
032198238X
ISBN 13:
978-0-32198-238-4
Chapter 2 - Matrix Algebra - 2.9 Exercises - Page 160: 16
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