Suppose that the voltage vector of the heart vt changes from one beat to the next according to the equation vt + 1 = 1 0 0 −1 vt. If the voltage vector during the current heartbeat is 0.9 −0.4 , what was the voltage vector in the previous heartbeat?

Engines for propeller-driven aircraft are limited in their maximum rotational speed by the fact that the tip speed of the propeller must not approach the speed of sound in air (mach i). taking 6 ft as a typical diameter for a propeller of a light airplane and 1100 fils as the speed of sound, find the upper limit on the rpm (revolutions per minute) of the propeller shaft.