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LAS VEGAS (AFP) — Children may not like it but a British technology firm has invented an electronic babysitter -- a wristwatch-like device that lets parents know where their children are at all times. The GPS Child Locator, or num8, attaches securely to a child’s wrist and contains a Global Positioning System (GPS), said Matthew Salmon, a spokesman for the manufacturer, lok8u. It uses GPS and GSM (Global System for Mobiles) technology with an accuracy of 10 feet (three meters), he said. It tracks your child. It only starts working when the device is connected to the child’s wrist, Salmon两条边是6和8的直角三角形，其内切圆的半径是    ．