Help: What is the length of [BP]?

What is the length of [BP]

Having no information regarding B, P, or what you mean by the "length" of the matrix BP, it is not possible to say. (Also, is BP a product matrix?)

Kindly please reply with the full text of the exercise, along with a clear listing of your thoughts and efforts so far. Thank you!
 
What is the length of [BP]
I presume [BP] in your notation means the segment with endpoints B and P. Then the length of [BP] is the distance between those points.

In order to say any more, we'd need to know something about the points, such as their coordinates, or a figure containing them. What else are you told?
 
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