數學知識交流---求值(1)

(1) 解：
4x + 7y + 9z = 104 ------(1)
8x - 2y + 3z = 113 -------(2)
(2) × 3 - (1)，得：
20x -13y = 235

(2) 解：
√[(x+6)(x+2)]+√[(x-6)(x-2)] = 24
(√[(x+6)(x+2)])+√[(x-6)(x-2)])² = 24²
(x+6)(x+2) + (x-6)(x-2) + 2√[(x+6)(x+2)(x-6)(x-2)] = 576
x² + √[(x²-36)(x²-4)] = 276
(x² - 36)(x² - 4) = (276 - x)²
x^4 - 40x² + 144 = x^4 - 552x² + 76176
512x² = 76032
x² = 148.5
把x² = 148.5代入√[(x+4)(x-4)]，得：
√[(x+4)(x-4)]
= √(x² - 16)
= √(148.5 - 16)
= (√530) / 2