Помогите,мозги вообще не варят , с 433 по 440

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$433.\;\frac{48x^2}{6x+4}-8x=\frac{48x^2-8x(6x+4)}{6x+4}=\frac{48x^2-48x^2-32x}{2(3x+2)}=\frac{-32x}{2(3x+2)}=-\frac{16x}{3x+2}\\\\434.\;\frac{20x^2}{2x-9}-10x=\frac{20x^2-10x(2x-9)}{2x-9}=\frac{20x^2-20x^2+90x}{2x-9}=\frac{90x}{2x-9}\\\\435.\;\frac{50x^2}{5x+10}-10x=\frac{50x^2-10x(5x+10)}{5x+10}=\frac{50x^2-50x^2-100x}{5(x+2)}=\frac{-100x}{5(x+2)}=-\frac{20x}{x+2}$

$436.\;\frac2a-\frac{-2a^2+9b^2}{ab}-\frac{2a}b=\frac2a+\frac{2a^2-9b^2}{ab}-\frac{2a}b=\frac{2b+2a^2-9b^2-2a^2}{ab}=\\=\frac{2b-9b^2}{ab}=\frac{b(2-9b)}{ab}=\frac{2-9b}a\\\\437.\;\frac6a-\frac{-5a^2+5b^2}{ab}-\frac{5a}b=\frac6a+\frac{5a^2-5b^2}{ab}-\frac{5a}b=\frac{6b+5a^2-5b^2-5a^2}{ab}=\\=\frac{6b-5b^2}{ab}=\frac{b(6-5b)}{ab}=\frac{6-5b}a$

$438.\;\frac2a-\frac{-3a^2-10b^2}{ab}-\frac{3a}b=\frac2a+\frac{3a^2+10b^2}{ab}-\frac{3a}b=\frac{2b+3a^2+10b^2-3a^2}{ab}=\\=\frac{2b+10b^2}{ab}=\frac{b(2+10b)}{ab}=\frac{2+10b}a\\\\439.\;\frac6a-\frac{-6a^2-8b^2}{ab}-\frac{6a}b=\frac6a+\frac{6a^2+8b^2}{ab}-\frac{6a}b=\frac{6b+6a^2+8b^2-6a^2}{ab}=\\=\frac{6b+8b^2}{ab}=\frac{b(6+8b)}{ab}=\frac{6+8b}a\\\\440.\;\frac7a-\frac{-10a^2-11b^2}{ab}-\frac{10a}b=\frac{7b+10a^2+11b^2-10a^2}{ab}=\frac{b(7+11b)}{ab}=\frac{7+11b}a$