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题目已知a=(2,-1),b=(-1,3),c=xa-yb.若y=2,且(a+b)∥c,求x. 它是一道测验题,考试时,我想到以下简解: 因a与b不共线,a与b可作为基底. 将a+b视作(1,1),而c=xa-2b视作(x,-2), 则(1,1)∥(x,-2),
The title is known as a=(2,-1), b=(-1,3),c=xa-yb. If y=2, and (a+b)∥c, find x. It is a quiz question. During the exam, I thought of the following brief explanation: Because a and b are not collinear, a and b can be used as the basis. Treat a+b as (1,1), and c=xa-2b as (x,-2) ,(1,1)∥(x,-2),