How do we determine whether circuit element is negative or positive?

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asd852
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Homework Statement
How do we determine whether this element in circuit is negative or positive(Nodal analysis)?
Relevant Equations
Nodal analysis
Circuit schematic with nodal analysis working: 20 V source, 20 Ω, 10 V source across a supernode (V1, V2), 20 Ω, 10 Ω, 5 Ω, 9 A source and 10 Ω, with red annotations and the node 3 equation written below.
 
Attachments
  • Handwritten nodal analysis working on lined paper: node 3 equations written as i_4 + g + i_5 = 0, with i_4 = (v_2 - v_3)/5 and i_5 = v_3/10, and a few crossed-out lines above.
    IMG_20201129_224636.jpg
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Discussion

Aren't the +- signs on the selected voltage source enough?
 
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