f(x) = -4x + 1 = 1 - 4x
f(x) = 0: 1 - 4x = 0, x = 1/4
f(x) > 0: 1 - 4x > 0, x < 1/4
f(x) < 0: 1 - 4x < 0, x > 1/4
f(x) = -4x + 1 = 1 - 4x
f(x) = 0: 1 - 4x = 0, x = 1/4
f(x) > 0: 1 - 4x > 0, x < 1/4
f(x) < 0: 1 - 4x < 0, x > 1/4