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What else can I help you with?
Let A be a 6by4 matrix and B a 4by6 matrix show that the 6by6 matrix AB can not be invertible?
It is not possible to show that since it is not necessarily true.There is absolutely nothing in the information that is given in the question which implies that AB is not invertible.
What is the difference between a 6by4 tractor unit and a6by2 tractor unit?
A 6x4 tractor has three axles (one steer axle and two drive axles). In normal operations, only one drive axle is engaged, but the second axle can be engaged as well using a differential lock. 6x2 tractors are more common in Europe, Asia, Northern Africa, etc. They will have a steer axle, and a single drive axle. They will also have an additional axle next to the drive axle, which cannot be engaged to drive the vehicle. Often, this will be a lifting 'tag' axle, which in Europe would usually have one tire on either side, while some of Schneider National's Freightliner Argosy tractors in the US and Canada have a lifting rear axle with two tires per side to allow the same weight rating as if it were a drive axle.
