Vt = [[1, 0], [0, -1]] Vt-1. If the voltage vector during the current heartbeat is [0.5, -0.4], what was the voltage vector in the previous heartbeat?
a) [0.5, -0.4]
b) [0.5, 0.4]
c) [-0.5, 0.4]
d) [-0.5, -0.4]