\[\boxed{\text{322\ (322).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ 80 + y^{2} = 81\]
\[y^{2} = 81 - 80\]
\[y^{2} = 1\]
\[y = \pm \sqrt{1}\]
\[y = \pm 1.\]
\[\textbf{б)}\ 19 + c^{2} = 10\]
\[c^{2} = 10 - 19\]
\[c^{2} = - 9 < 0\]
\(c = \varnothing\).
\[\textbf{в)}\ 20 - b^{2} = - 5\]
\[b^{2} = 20 + 5\]
\[b = 25\]
\[b = \pm \sqrt{25}\]
\[b = \pm 5.\]
\[\textbf{г)}\ 3x^{2} = 1,47\]
\[x^{2} = 1,47\ :3\]
\[x^{2} = 0,49\]
\[x = \pm \sqrt{0,49}\]
\[x = \pm 0,7.\]
\[\textbf{д)}\ \frac{1}{4}a^{2} = 10\]
\[a^{2} = 10\ :\frac{1}{4} = 10 \cdot 4\]
\[a^{2} = 40\]
\[a = \pm \sqrt{40}\]
\[a = \pm 2\sqrt{10}.\]
\[\textbf{е)} - 5y^{2} = 1,8\]
\[y^{2} = 1,8\ :( - 5) < 0\]
\[y = \varnothing.\]