题目

It is commonly known that Japan went from a 19th century national economy to a 20th century global economy in a time span of 30 years between 1945 and 1975. What is less known is that Japan, understanding that fast, efficient transport was the key to a global economy, was the first country in the world to introduce the “Bullet Train”. Kawasaki Heavy Industries was duly appointed the manufacturer and the first high speed train went “on line” in 1964. The Shinkansen, as is known in Japan, made its first journey between her capital and Osaka, a distance of 301 miles, at a speed of 132 mph如图，在△ABC中，AB=AC，AB的垂直平分线交AB、AC于D、G，AB=10cm，△BGC的周长为17cm，求BC的长．