急,大家可唔可以教吓我解方程啊4
2008-09-07 8:08 pm
解下列各方程 , 方法不限
11. 6 + 4x - 16x2 = 0
12. 5x2 - 30 =0
用公式求根法解下列各方程 (如有需要,答案以根號表示,並指出沒有實根的方程)
13. 4x2 - 0.6x -0.5 = 0
14. 50x2 - 40x +8 = 0
15. √5x = 3/2 (x2 - 4)
回答 (1)
2008-09-07 9:16 pm
✔ 最佳答案
11. -2(-3 - 2x + 8x^2) = 0-2(4x - 3)(2 x+1) = 0
x = 3/4 and -1/2.
12.
5x ^2 = 30
x^2 = 6
x = sqrt 6 and - sqrt 6.
13.
4x^2 -0.6x - 0.5 = 0
40x^2 - 6x - 5 = 0
x = [6 +/- sqrt(36 + 800)]/80 = [6 +/- 2sqrt 209]/80 = [3 +/- sqrt 209]/40.
14.
50x^2 - 40x + 8 = 0
25x^2 - 20x + 4 = 0
(5x - 2)^2 = 0
x = 2/5.
15.
(2sqrt 5)x = 3x^2 - 12
3x^2 - (2sqrt5)x - 12 = 0
x = [2sqrt 5 +/- sqrt(20 + 144)]/6 = [sqrt 5 +/- sqrt 41]/3.
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