Question

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(C) EF
EC AE=FC
(D) EF
EC AE FC
5. △ABC的三邊長為a、b、c,且a+b+c+x-ba-14b-2cx+58=0,則a=
b=
;x的範圍是
>
9
EKONOMIA E 04-837

Answer 1

Mer

2cx = a^2 - 6a + b^2 -14b + c^2 + 58
x = (a^2 - 6a + b^2 -14b + c^2 + 58)/2c
x = [(a - 3)^2 + (b - 7)^2 + c^2]/2c
當a = 3，b = 7時，c = 2x
7-3 < 2x < 7+3
2 < x < 5

Mer

漏看了不好意思~~
a^2 - 6a + b^2 -14b + c^2 -2cx + x^2 = -58
(a - 3)^2 + (b - 7)^2 + (c - x)^2 = 0
因為平方≧0，所以a = 3，b = 7，c = x
7-3 < x < 7+3
4 < x < 10