3. Решите уравнение: a) x² - 35² = 0 б) 25 - 81y2 = 0 в) (7-y)²-у(у+1,5)=49

a)
\[x^2 - 35^2 = 0\]
\[x^2 = 35^2\]
\[x = \pm 35\]

б)
\[25 - 81y^2 = 0\]
\[81y^2 = 25\]
\[y^2 = \frac{25}{81}\]
\[y = \pm \frac{5}{9}\]

в)
\[(7-y)^2 - y(y + 1.5) = 49\]
\[49 - 14y + y^2 - y^2 - 1.5y = 49\]
\[-14y - 1.5y = 0\]
\[-15.5y = 0\]
\[y = 0\]

**Ответ:**
a) \[x = \pm 35\]
б) \[y = \pm \frac{5}{9}]
в) \[y = 0\]