计量问题，该如何证明矩阵是正定的强结果?

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  1. For the F statistic to be well-defined, the matrix R( X'x) R' must be nonsingular. Prove the stronger result that the matrix is positive definite
    为了使F统计量得到良好定义，矩阵R（X'X）R'必须是非奇异的。证明矩阵是正定的强结果

正定矩阵的几种经典证法：
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