Which calculation is used when √3 becomes √4 in a square-root spiral?

Correct answer: (√3)² + 1² = 4

The governing concept is the Pythagorean theorem. In the square-root spiral, the existing hypotenuse √3 becomes one perpendicular side of the next right triangle, and a new perpendicular segment of length 1 unit is added. If H is the new hypotenuse, then H² = (√3)² + 1² = 3 + 1 = 4. Taking the positive square root gives H = √4, so option A is the correct calculation. Option C is invalid because lengths cannot be combined in that way to represent a right-triangle hypotenuse. Option B uses a segment of length 3 instead of 1 and gives √12. Option D subtracts squares, whereas the Pythagorean theorem requires addition of the squares of perpendicular sides.