realizar las siguientes sumas
[tex](5x {}^{2} + 7x + 8) + (3x + 9)[/tex]
[tex](4m {}^{2} - 2mn - 5n) + (6m {}^{2} + 7mn)[/tex]
[tex]( - 9a {}^{3} b {}^{2} + 7a {}^{2} b - 6) + (12a {}^{3} b {}^{2} - 9a {}^{2} b - 5)[/tex]

[tex]( - 15xy {}^{2} + 8x {}^{2} y - 9x) + ( - 18x {}^{2} y - 3x + 6)[/tex]
[tex]( \frac{1}{2} m {}^{3} - \frac{ 2}{3} m {}^{2} ) + ( - \frac{2}{5} m {}^{3} + \frac{1}{6} m2)[/tex]

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