3. Решите уравнение: a) 4²-x²= 0 б) 81y²-16 = 0 в) (9-x)²-x(x+8,5)=81

a) $$4^2 - x^2 = 0$$ $$16 - x^2 = 0$$ $$x^2 = 16$$ $$x = \pm \sqrt{16}$$ $$x = \pm 4$$ б) $$81y^2 - 16 = 0$$ $$81y^2 = 16$$ $$y^2 = \frac{16}{81}$$ $$y = \pm \sqrt{\frac{16}{81}}$$ $$y = \pm \frac{4}{9}$$ в) $$(9-x)^2 - x(x+8,5) = 81$$ $$81 - 18x + x^2 - x^2 - 8,5x = 81$$ $$81 - 26,5x = 81$$ $$-26,5x = 0$$ $$x = 0$$ Ответ: a) $$x = \pm 4$$ б) $$y = \pm \frac{4}{9}$$ в) $$x = 0$$