中四數學!!!!超急!!!!plz

2009-01-07 5:35 pm
用配方法解2x既2次方=7x-1
點計- -"?

回答 (2)

2009-01-07 10:45 pm
✔ 最佳答案
2x^2 = 7x - 1
2x^2 - 7x = -1
2(x^2 - 7/2 x) = -1
2(x^2 - 7/2 x + (7/4)^2) = (7/4)^2 - 1
2(x^2 - 7/2 x + 49/16) = 49/8 - 1
2(x - 7/4)^2 = 41/8
(x - 7/4)^2 = 41/16
x - 7/4 = √(41/16) 或 x - 7/4 = -√(41/16)
x - 7/4 = (√41)/4 或 x - 7/4 = -(√41)/4
x = (√41+7)/4 或 x = -(√41+7)/4
參考: oxford
2009-01-07 5:52 pm
2x2 = 7x-1
2x2-7x+1= 0
x = {-(-7) +/- √[(-7)2-4(2)(1)]} / 2(2)
x = 7/4 +/- √(41)/4
x = 0.15 or x = 3.35
參考: myself


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