The answer is C.
You need you use Pythagoras theorem 2 times to have 2 equations with the same sides i.e. for example a2 + b2 = 81 and a2 - b2 = 9.
You can do it as you have different triangles but with the same sides.
Arithmetic sequence: must have a constant common difference.
3/20-1/10=(3-2)/20=1/20
5/30-3/20=(10-9)/60=1/60
Difference is not constant, so no.
Geometric sequence: must have a common ratio
30/20 / (1/10) = 15
5/30 / (3/20) = 100/90 = 10/9
ratio is not constant, so no.
The answer is (c) neither geometric nor arithmetic
