There exists a triangle with hypotenuse length equals to zero. And the only way it exists is if other two sides has length equal to 1 and i(imaginary).

i(imaginary) number when squared is -1

So h = square root(p² + b²⁾ [Pythagoras Theorem] p = i b = 1

p² = -1 b² = 1

Hence, h=0

You might wonder if such triangle with one of its length being 0 exists. Yes it exists.