F.4 一元二次方程

1)
(k - 3)(k + 0.2) - 1 = 2(k - 1)

k^2 - 3k + 0.2k - 1.6 = 2k - 2

k^2 - 2.8k - 2k + 0.4 = 0

k^2 - 4.8k + 0.4 = 0

5k^2 - 24k + 2 = 0

k = 24 +- sqrt(576 - 40) / 10

= 24 +- sqrt(536) / 10

= 4.715........ or 0.084......

= 4.72 or 0.08



2010-09-19 22:10:06 補充：
sorry

2)
3x^2 - 6x - 45 = 0

3(x^2 - 2x - 15) = 0

3(x - 5)(x + 3) = 0

x = 5 or -3

3)
3x^2 - 48 = 0

3(x^2 - 16) = 0

3(x - 4)(x + 4) = 0

x = 4 or -4