己知 f (x) = x^2 - kx
a. 求 f (x+2) 和 f (x-2) 的值
b.若 f (x+2) - f (x-2) = kx-32 ,求k 的值
c. 由此,若 f (x+2) = f (x-2) + 40 ,求x 的值
答案
a. f (x+2) = x^2 + (4-k)x + 4 - 2k
f (x -2)= x^2 - (4+k)x + 4 + 2k
b. 8
c. 9
本人只要b同c的列式
數學問題一條(凼數)(須列式)(20分)
2007-10-01 12:05 am
回答 (1)
2007-10-01 12:22 am
✔ 最佳答案
a.f(x+2)=x^2 + (4-k)x + 4 - 2k
f(x-2)
= x^2 - (4+k)x + 4 + 2k
b.
.............................f (x+2) - f (x-2) = kx-32
x^2+(4-k)x+4-2k-(x^2-(4+k)x+4+2k)=kx-32
...........................................8x-4k=kx-32
..........................................k(4+x)=8(x+4)
..................................................k=8
c.
......... f (x+2) = f (x-2) + 40
f (x+2) - f (x-2)=40
............8x-32 =40
....................x=9
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