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標題:

A. maths (F.4) 急急急

發問:

Given that the quadratic equation x^2+kx-(k-3)=0 has real roots a and b . If lal=lbl, find the values of k . (It is an absloute number) 更新: 個答案係 -6 or 2

最佳解答:

Given that the quadratic equation x2+kx-(k-3)=0 has real roots a and b . If lal=lbl, find the values of k . 若 │a│=│b│則 a = b 或 a = -b 若 a = b 則有重根則 判別式 B2 – 4AC = 0 k2 – 4(1)(k-3) = 0 k2 – 4k + 12 = 0 但因k2 – 4k + 12 = 0 的判別式大於零所以無解。 若 a = -b 則 a + b = -k 但 a = - b 即 k = 0

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