If the triangle is a right triangle, then
(3x)² + x² = (10)² .
9x² + x² = 100
10x² = 100
x² = 10
x = √10 = approx. 3.1622...
If ' x ' is anything less than √10 , then the short sides are too short
to make a right angle at the top, and the angle where they meet
is obtuse.
' x ' has to be greater than 2.5 ... otherwise the two short sides
can't stretch far enough to reach both ends of the long side (10) .
So, if 2.5 < x < √10 , then there is a triangle, and it's obtuse.