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原行列式 |A| =
|x+1 x+3 3|
|-4 2x+2 8|
|1 0 1-x|
|A| =
|x+1 x+3 2x+5|
|-4 2x+2 0|
|1 0 3-x|
|A| = 2(3-x)(x+1)^2 - 2(x+1)(2x+5) + 4(3+x)(3-x) = 0
即 (3-x)(x+1)^2 - (x+1)(2x+5) + 2(3+x)(3-x) = 0
x^3 + 3x^2 + 2x -16 = 0
x1+x2+x3 = -3
|x+1 x+3 3|
|-4 2x+2 8|
|1 0 1-x|
|A| =
|x+1 x+3 2x+5|
|-4 2x+2 0|
|1 0 3-x|
|A| = 2(3-x)(x+1)^2 - 2(x+1)(2x+5) + 4(3+x)(3-x) = 0
即 (3-x)(x+1)^2 - (x+1)(2x+5) + 2(3+x)(3-x) = 0
x^3 + 3x^2 + 2x -16 = 0
x1+x2+x3 = -3
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