$\frac{1}{16}a^2 - \frac{1}{25} = 0$
$(\frac{1}{4}a)^2 - (\frac{1}{5})^2 = 0$
$(\frac{1}{4}a - \frac{1}{5})(\frac{1}{4}a + \frac{1}{5}) = 0$ | * 20
(5a − 4)(5a + 4) = 0
5a − 4 = 0
5a = 4
$a = \frac{4}{5}$
или
5a + 4 = 0
5a = −4
$a = -\frac{4}{5}$
Ответ: $-\frac{4}{5}; \frac{4}{5}$.

$\frac{4}{49}b^2 - \frac{16}{121} = 0$
$(\frac{2}{7}b)^2 - (\frac{4}{11})^2 = 0$
$(\frac{2}{7}b - \frac{4}{11})(\frac{2}{7}b + \frac{4}{11}) = 0$ | * 77
(22b − 28)(22b + 28) = 0
22b − 28 = 0
22b = 28
$b = \frac{28}{22} = \frac{14}{11} = 1\frac{3}{11}$
или
22b +28 = 0
22b = −28
$b = -\frac{28}{22} = -\frac{14}{11} = -1\frac{3}{11}$
Ответ: $-1\frac{3}{11}; 1\frac{3}{11}$.

$\frac{9}{16}c^2 - \frac{81}{100} = 0$
$(\frac{3}{4}c)^2 - (\frac{9}{10})^2 = 0$
$(\frac{3}{4}c - \frac{9}{10})(\frac{3}{4}c + \frac{9}{10}) = 0$ | * 20
(15c − 18)(15c + 18) = 0
15c − 18 = 0
15c = 18
$c = \frac{18}{15} = \frac{6}{5} = 1\frac{1}{5}$
или
15c + 18 = 0
15c = −18
$c = -\frac{18}{15} = -\frac{6}{5} = -1\frac{1}{5}$
Ответ: $-1\frac{1}{5}; 1\frac{1}{5}$.

$\frac{36}{1225}d^2 - \frac{64}{441} = 0$
$(\frac{6}{35}d)^2 - (\frac{8}{21})^2 = 0$
$(\frac{6}{35}d - \frac{8}{21})(\frac{6}{35}d + \frac{8}{21}) = 0$ | * 105
(18d − 40)(18d + 40) = 0
18d − 40 = 0
18d = 40
$d = \frac{40}{18} = \frac{20}{9} = 2\frac{2}{9}$
или
18d + 40 = 0
18d = −40
$d = -\frac{40}{18} = -\frac{20}{9} = -2\frac{2}{9}$
Ответ: $-2\frac{2}{9}; 2\frac{2}{9}$.