Answer:
d. 6
Step-by-step explanation:
The product of lengths to the near and far intersection points is the same for both secants:
PB×PA = PD×PC
We can use this relation to solve for x, then use the value of x to find PD.
7×12 = (3x)(7x)
4 = x² . . . . . . . . . divide by 21
2 = x . . . . . . . . . . take the square root
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PD = 3x = 3·2
PD = 6
