问题
选择题
方程组
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答案
把
代入方程组x=2 y=3
得a=2，b=2，ax-y=1 x+by=8
所以方程x2+ax+b=0变为x2+2x+2=0，其中a=1，b=2，c=2，
∴△=b2-4ac=22-4×1×2=-4＜0，
∴方程没有实数根
故选C
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方程组
|
把
代入方程组x=2 y=3
得a=2，b=2，ax-y=1 x+by=8
所以方程x2+ax+b=0变为x2+2x+2=0，其中a=1，b=2，c=2，
∴△=b2-4ac=22-4×1×2=-4＜0，
∴方程没有实数根
故选C
"Efficiency is the by-product of comfort," says Dr. Erwin Tichauer of New York University. To prove this____, Dr. Tichauer uses his capability to find_____ways to do things. _____, he felt that the traditional kind of pliers(钳子）______a better design. The usual____limited hand movement and used unnecessary force because it bent the_____. So he designed a pair of pliers to allow the wrist to remain in a comfortable position. To improve the design of______and then make work easier, Dr. Tichauer____the old tools. He asks such questions as: why ____a stepladder have four legs____three are more stable? Why dose a screwdriver (螺丝刀) have to be made with straight handles? After testing his____, he has invented a new tool that causes less muscle injury and is more efficient. Tichauer is not interested in getting ____ from his inventions. In fact, he says, "We _____ people to steal from us. At New York University, we do not patent(注册专利）knowledge or invention."__ __companies have adopted some of his inventions. As a biochemist, as well as inventor, Dr Techauer____the effect of stress on areas of the body. Even easy______work may put heavy stress on small areas of body and____causes a serious disease. Thus his studies of workers in factories who use the____tool all day long are extremely____in learning about the damage on human body? Dr. Techauer knows that he can not redesign the ____ so he redesigns the tool!
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