问题
选择题
边长为10米的正方形，要使它的面积扩大到原来的4倍，它的边长应增加（ ）
A．4米
B．8米
C．10米
D．12米
答案
设它的边长应增加x米，则后来的边长为：（10+x）米，
由题意得：（10+x）2=4×102
∴x1=10，x2=-30，
∵x2=-30，不符合题意，故舍去，
∴x=10．故选C．
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边长为10米的正方形，要使它的面积扩大到原来的4倍，它的边长应增加（ ）
A．4米
B．8米
C．10米
D．12米
设它的边长应增加x米，则后来的边长为：（10+x）米，
由题意得：（10+x）2=4×102
∴x1=10，x2=-30，
∵x2=-30，不符合题意，故舍去，
∴x=10．故选C．
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| Elizabeth Clay decided to go home and spend the holiday with her parents. The next day she drove her old car home along the road. 1 she found she got a flat. The 22-year-old student 2 to stop her car by the side of the road in the winter night and opened the trunk. No 3 tire. At this time, a car 4 . Paul and Diane told Clay to 5 them to a service station near their 6 . They arrived to see that it had no suitable tires to 7 with her car. "Follow us home," said Paul. The couple called around to find a tire, No 8 . They decided to let her use their own car. "Here," Paul said, handing Clay a 9 of keys, "Take our car. We 10 be using it over the holiday." Clay was 11 . "But I'm going all the way to South Carolina, and I'll be gone for two weeks," she 12 them. "We know," Paul said. "We'll be 13 when you get back. Here's our number if you need to 14 us." Unable to believe her eyes, Clay watched as the 15 put her luggage into their car and then 16 her off. Two weeks later she 17 to find her old car cleaned inside and out with three new tires and the radio 18 . "Thank you so much," she said. "How much do I 19 you?" "Oh, no," Paul said, "we don't want any money. It's our 20 ." Clay realized that while it might have been their pleasure, it was now her duty to pass on their "do unto others" spirit. | ||||
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