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Answer:
x = 3
Explanation:
It is convenient to remember the ratios of side lengths of these "special triangles."
The side ratios of ΔABC are 1 : 1 : √2, so BC = AC/√2 = 6.
The side ratios of ΔBCD are 1 : √3 : 2, so BD = BC/2 = 6/2 = 3.
The value of x is 3.