Answer: 21xy√(2)
Explanation:
1: break down the square root and simplify the factors
7√(18x³y²) = 7√(9 * 2 * x² * x * y²)
2: simplify the square root by taking the square root of perfect squares within the radical
7 * 3 * √(2 * x² * x * y²)
3: take the square root of the perfect squares under the radical
21xy√(2)