Can you explain why it is impossible to construct this triangle?

Generate three random numbers to determine the side lengths of a triangle. What triangles can you draw?

What is the total area of the first two triangles as a fraction of the original A4 rectangle? What is the total area of the first three triangles as a fraction of the original A4 rectangle? If. . . .

Here is a chance to create some attractive images by rotating shapes through multiples of 90 degrees, or 30 degrees, or 72 degrees or...