If the length of two sides of a triangle are 5 & 11 , what is the range of possible lengths for the third side?

The minimum side length is where the triangle contracts to a line. This will be when 5 and the third side add up to 11, ie., the side is 6.

The maximum side length also flattens the triangle to a line, but now the 5 and 11 sides are aligned, and the third side overlays it, its length is 5+11=16.

So the range is [6,16]