设
，已知线性方程组Ax=b存在2个不同的解．
求λ，a；
参考答案：因为方程组Ax=b有2个不同的解，故[*]．
由
[*]
于是λ=1或λ=-1．
当λ=1时，r(A)=1，[*]，方程组Ax=b无解，舍去．
当λ=-1时，对Ax=b的增广矩阵作初等行变换
[*]
可见a=-2时，[*]，方程组Ax=b有无穷多解．故λ=-1，a=-2．
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| China is a large country of agriculture (农业). We all know that there are more than 800 million 1 in China. China starts to 2 the science of agriculture much earlier 3 other countries in the world. 4 people in Europe and America were trying to shoot wild animals and birds for food, farmers in China were 5 the science of agriculture. For example, Jia Sixie, who lived in the Northern Wei period (386-534AD), 6 one of the farming pioneers. After he finished his work in government, he 7 home and spent his time on research into agriculture. He 8 information, did experiments and learnt from the experience of farmers. He wrote a book called Qi Min Yao Shu. The book 9 has 110000 words is about both farming and gardening. This book is 10 to be an important summary (概要) of the knowledge of farming. | ||||
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