Short answer
What should you know first?
Span, independence, basis, and dimension become much easier on the GRE Mathematics Subject Test when you stop memorizing definitions and start treating vector spaces as structure. This page focuses on the linear-algebra language that sits right after matrices and systems.
What to study here
Focus on the moves that actually change later work.
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Decide whether a vector lies in the span of a set.
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Recognize linear dependence as redundancy.
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Find a basis for a familiar space or subspace.
Why it matters
Why this topic changes the rest of your prep.
These ideas answer four core linear-algebra questions: what can these vectors build, which ones are redundant, what is the smallest useful set, and how many degrees of freedom are really present.
Must know
Facts and heuristics that should start feeling automatic.
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In $$\mathbb{R}^n$$, any set with more than $$n$$ vectors is dependent.
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A set with fewer than $$n$$ vectors cannot span all of $$\mathbb{R}^n$$.
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A basis must be both minimal and complete.
Useful cue
Ask whether you are generating, testing dependence, or choosing coordinates.
Worked example
One representative example.
Does $$(2,3)$$ lie in the span of $$(1,1)$$ and $$(1,2)$$?
Long route
Set $$a(1,1)+b(1,2)=(2,3)$$ to get $$a+b=2$$ and $$a+2b=3$$. Subtract to find $$b=1$$, then $$a=1$$, so the vector lies in the span.
Fast route
Turn span membership into a small linear system, solve quickly, and verify a solution exists.
Common traps
What usually breaks first.
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Calling a spanning set a basis without checking independence.
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Forgetting that dependence means wasted information, not just similar-looking coordinates.
Quick questions
Short answers that searchers usually need first.
What should I study before span, basis, dimension for the GRE Mathematics Subject Test?
Before span, basis, dimension, steady Matrices and linear systems, Coordinate geometry and vectors in the plane so this topic does not turn into algebra or setup cleanup.
Why does span, basis, dimension matter on the GRE Mathematics Subject Test?
These ideas answer four core linear-algebra questions: what can these vectors build, which ones are redundant, what is the smallest useful set, and how many degrees of freedom are really present.
What does span, basis, dimension unlock after it gets stronger?
Span, basis, dimension unlocks Determinants and linear transformations, Eigenvalues, eigenvectors, diagonalization, Vectors, planes, and lines in 3D inside the same dependency-first study graph.