What is the square root of 16 x to the 36th power ?

The square root of 16 is 4. Also, √(x³⁶) = x¹⁸ because (x¹⁸)² = x³⁶ and x¹⁸ is nonnegative for real x. Therefore, √(16x³⁶) = 4x¹⁸, which is choice C.

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