Which is the correct calculation to make √2 in a square-root spiral?

Correct answer: √(1² + 1²)

The governing concept is the Pythagorean theorem applied to the first right triangle of the square-root spiral. The two perpendicular sides of that triangle each have length 1 unit. If h denotes the hypotenuse, then h² = 1² + 1² = 1 + 1 = 2. Taking the positive square root gives h = √2, so option A is the correct calculation. Option B uses two sides of length 2 and therefore gives √(4 + 4) = √8, not √2. Option C omits the required squaring of the perpendicular sides and is not the Pythagorean expression. Option D subtracts instead of adding and gives √1 = 1. Thus only option A correctly represents the first construction step.