所以答案是C
1 7/2 (a+b)/2
7/2 10 (5a+2b)/2
(a+b)/2 (5a+2b)/2 ab
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特征值是
0
[(ab+11)-√((a²+5)(b²+26))]/2
[(ab+11)+√((a²+5)(b²+26))]/2
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(ab+11)<√((a²+5)(b²+26))
所以一正一负一零
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C.