3. Решите уравнение: a) x² - 15² = 0 б) 49-36y² = 0 в) (9-y)²-у(у+1,9)=81

a) $$x^2 - 15^2 = 0 Rightarrow x^2 = 225 Rightarrow x = pm 15$$ б) $$49 - 36y^2 = 0 Rightarrow 36y^2 = 49 Rightarrow y^2 = rac{49}{36} Rightarrow y = pm rac{7}{6}$$ в) $$(9 - y)^2 - y(y + 1.9) = 81 Rightarrow 81 - 18y + y^2 - y^2 - 1.9y = 81 Rightarrow -19.9y = 0 Rightarrow y = 0$$