Question

subtraia -7a²+3a-9 de 5a²-6a-4.
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Answer 1

$7a^2+3a-9+5a^2-6a-4\\\\=7a^2+5a^2+3a-6a-9-4\\\\=12a^2+3a-6a-9-4\\\\=12a^2-3a-9-4\\\\\mathrm{Subtrair:}\:-9-4=-13\\\\=12a^2-3a-13$