To make √32 in a square root spiral, which hypotenuse is used immediately before it?

Correct answer: √31

The governing construction rule is that a unit perpendicular is added to the current hypotenuse. If the current hypotenuse is √n, the next hypotenuse has length √(n + 1), because h² = (√n)² + 1² = n + 1. To obtain √32, the preceding value must therefore have n + 1 = 32. Solving gives n = 31, so the immediately previous hypotenuse is √31. Option B is correct. √30 would lead to √31, not √32. √32 is the target itself rather than the previous hypotenuse, while √33 comes after the target in the sequence. The answer follows from the construction, not from subtracting ordinary lengths.