請幫我用多項式解題拜託! 1. x^2+8x+15=(x-k)^2-1，則k=?
回答 (2)
2017-08-17 6:03 pm
✔ 最佳答案
Solx^2+8x+15
=(x^2+8x)+15
=(x^2+2*x*4)+15
=(x^2+2*x*4+16)+15－16
=(x+4)^2－1
k=－4
2017-08-17 6:07 pm
x² + 8x + 15 = (x-k)² -1
x² + 8x + 15 = x² -2kx + k² -1
=> 8x = -2kx . . . . . . . . . . . . .①
=> 15 = k² -1 . . . . . . . . . . . . ②
從 ① 8 = -2k => k = -4
從 ② 15 = k² -1 => k² =16 => k = ± 4
k = -4 或 k = 4 (rejected)
∴ k = -4 (Ans)
x² + 8x + 15 = x² -2kx + k² -1
=> 8x = -2kx . . . . . . . . . . . . .①
=> 15 = k² -1 . . . . . . . . . . . . ②
從 ① 8 = -2k => k = -4
從 ② 15 = k² -1 => k² =16 => k = ± 4
k = -4 或 k = 4 (rejected)
∴ k = -4 (Ans)
收錄日期: 2021-04-30 22:28:54
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