簡易方程數學問題

(a)
2u² -7u -15 = 0
(2u + 3)(u - 5) = 0
u = 5 or u = -3/2

(b)
題目應該是 2(x²-4x)² - 7(x²-4x) - 15 = 0

那麼 Let u = x² - 4x

2(x²-4x)² - 7(x²-4x) - 15 = 0
變成
2u² - 7u - 15 = 0
u = 5 or u = -3/2 [from (a)]
即是
x² - 4x = 5 or x² - 4x = -3/2
x² - 4x - 5 = 0 or 2x² - 8x + 3 = 0
(x - 5)(x + 1) = 0 or 2x² - 8x + 8 = 5
x = 5 or x = -1 or 2(x² - 4x + 4) = 5
x = 5 or x = -1 or 2(x - 2)² = 5
x = 5 or x = -1 or (x - 2)² = 5/2
x = 5 or x = -1 or x - 2 = ±√(5/2)
x = 5 or x = -1 or x = 2 ± √(5/2)

－－－－－－－－－－－－－－－－－－－－

如果題目真是

2(x²-4x) - 7(x²-4x) - 15 = 0

那就跟 (a) 無關。

快去這里*****我每次都是去這里看
価儬号剭僢