3. Решите уравнение: a) x2 - 52 = 0 б) 25 - 49y2 = 0 в) (3-y)²-у(у+4,7)=9

a) $$x^2 - 5^2 = 0$$ $$x^2 = 25$$ $$x = \pm 5$$ б) $$25 - 49y^2 = 0$$ $$49y^2 = 25$$ $$y^2 = \frac{25}{49}$$ $$y = \pm \frac{5}{7}$$ в) $$(3-y)^2 - y(y+4.7) = 9$$ $$9 - 6y + y^2 - y^2 - 4.7y = 9$$ $$-10.7y = 0$$ $$y = 0$$