[tex]13.d) 2(x - 3) {}^{2} - 21 \leqslant (2x - 5) {}^{2} - 2x {}^{2} = > 2(x {}^{2} - 6x + 9) - 21 \leqslant 4x {}^{2} - 20x + 25 - 2x {}^{2} = > 2x {}^{2} - 12x + 18 - 21 \leqslant 2x {}^{2} - 20x + 25 = > 2x {}^{2} - 12x - 3 \leqslant 2x {}^{2} - 20x + 25 = > - 12x - 3 \leqslant - 20x + 25 = > - 12x + 20x \leqslant 25 + 3 = > 8x \leqslant 28 = > x \leqslant \frac{7}{2} = > [/tex]
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[tex]( - \infty . \frac{7}{2} [/tex]
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