а) (2x-1)^2 = 0
2x - 1 = 0
2x = 1
x = 1/2

б) x^2 - 10x + 25 = 0
(x - 5)^2 = 0
x - 5 = 0
x = 5

в) 4x^2 + 12x + 9 = 0
(2x + 3)(2x + 3) = 0
2x + 3 = 0
2x = -3
x = -3/2

г) 5t^2 + 20t + 20 = 0
5(t^2 + 4t + 4) = 0
5(t + 2)(t + 2) = 0
t + 2 = 0
t = -2

д) 2x^2 - 12x + 18 = 0
2(x^2 - 6x + 9) = 0
2(x - 3)(x - 3) = 0
x - 3 = 0
x = 3

е) -9a^2 - 12a - 4 = 0
-9a^2 - 6a - 6a - 4 = 0
-3a(3a + 2) - 2(3a + 2) = 0
(3a + 2)(-3a - 2) = 0
3a + 2 = 0 or -3a - 2 = 0
3a = -2 or -3a = 2
a = -2/3 or a = -2/3

Итак, решения уравнений:
а) x = 1/2
б) x = 5
в) x = -3/2
г) t = -2
д) x = 3
е) a = -2/3, a = -2/3