Уровень 3. 4. Упростите выражение: a) (7-2x)(7+2x)-(x-8)(8+x)-(4-3x)(5+3x); б) 16-(6-11x)²=0; в) (7m-13)²-(9m+19)²=0;

a) $(7-2x)(7+2x) - (x-8)(8+x) - (4-3x)(5+3x) = 49 - 4x^2 - (x^2 - 64) - (20 + 12x - 15x - 9x^2) = 49 - 4x^2 - x^2 + 64 - 20 + 3x + 9x^2 = 4x^2 + 3x + 93$ б) $16 - (6-11x)^2 = 0 \Rightarrow (6-11x)^2 = 16 \Rightarrow 6-11x = \pm 4 \Rightarrow -11x = -6 \pm 4 \Rightarrow -11x = -2 \lor -11x = -10 \Rightarrow x = \frac{2}{11} \lor x = \frac{10}{11}$ в) $(7m-13)^2 - (9m+19)^2 = 0 \Rightarrow (7m-13 - (9m+19))(7m-13 + 9m+19) = 0 \Rightarrow (-2m - 32)(16m + 6) = 0 \Rightarrow m = -16 \lor m = -\frac{3}{8}$