To solve these quadratic equations, we can use the quadratic formula.

For the first equation, x^4 - 3x^2 - 28 = 0:
a = 1, b = -3, c = -28

x = (-b ± √(b^2 - 4ac)) / 2a
x = (3 ± √(9 + 112)) / 2
x = (3 ± √121) / 2
x = (3 ± 11) / 2

So, x = 7 or x = -4

For the second equation, x^4 - 14x^2 - 32 = 0:
a = 1, b = -14, c = -32

x = (14 ± √(196 + 128)) / 2
x = (14 ± √324) / 2
x = (14 ± 18) / 2

So, x = 16 or x = -2

For the third equation, x^4 - 4x^2 - 45 = 0:
a = 1, b = -4, c = -45

x = (4 ± √(16 + 180)) / 2
x = (4 ± √196) / 2
x = (4 ± 14) / 2

So, x = 9 or x = -5

Therefore, the solutions to the quadratic equations are:
For x^4 - 3x^2 - 28 = 0: x = 7, x = -4
For x^4 - 14x^2 - 32 = 0: x = 16, x = -2
For x^4 - 4x^2 - 45 = 0: x = 9, x = -5