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We develop some basic tools to work with representable matroids of bounded tree-width and use them to prove that, for any prime power class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0195669816300701&_mathId=si2.gif&_user=111111111&_pii=S0195669816300701&_rdoc=1&_issn=01956698&md5=500f4f1d4b70279d29e69ea585267d30" title="Click to view the MathML source">qclass="mathContainer hidden">class="mathCode"> and constant class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0195669816300701&_mathId=si3.gif&_user=111111111&_pii=S0195669816300701&_rdoc=1&_issn=01956698&md5=b335fbcefa9c34c0d6e41e8a26f667e4" title="Click to view the MathML source">kclass="mathContainer hidden">class="mathCode">, the characteristic polynomial of any loopless, class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0195669816300701&_mathId=si4.gif&_user=111111111&_pii=S0195669816300701&_rdoc=1&_issn=01956698&md5=463f85249ecef21aa5bc44ae88b93bbe" title="Click to view the MathML source">GF(q)class="mathContainer hidden">class="mathCode">-representable matroid with tree-width class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0195669816300701&_mathId=si3.gif&_user=111111111&_pii=S0195669816300701&_rdoc=1&_issn=01956698&md5=b335fbcefa9c34c0d6e41e8a26f667e4" title="Click to view the MathML source">kclass="mathContainer hidden">class="mathCode"> has no real zero greater than class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0195669816300701&_mathId=si6.gif&_user=111111111&_pii=S0195669816300701&_rdoc=1&_issn=01956698&md5=b2be0f04d393cdfcf379c76b4e8bcd2c" title="Click to view the MathML source">qk−1class="mathContainer hidden">class="mathCode">.