有兩條a.maths 唔識(5分)

1) |x| + 9 = 8
|x|=-1
the equation has no roots since|x|≧0 for all x

2) | (3 + 2x)/(5x - 8)|= 2 / 5
(3 + 2x)/(5x - 8)=2/5 or (3 + 2x)/(5x - 8) =-2/5
5(3+2x)=2(5x-8) or 5(3+2x)=2(8-5x)
15+10x=10x-16 or 15+10x=16-10x
15=-16 (no solution) or 20x=1
x=1/20




3) x^2 - |x| - 12 = 0
|x|^2-|x|-12=0 (x^2=|x|^2)
(|x|+3)(|x|-4)=0
|x|=-3 (rejected) or |x|=4
x=4 or x=-4

1) |x| = -1(rej.)
so no soution
2) (3 + 2x)/(5x - 8)=+2 / 5 or (3 + 2x)/(5x - 8)= -2 / 5
3 + 2x=2x-16/5 or 3 + 2x=-2x+16/5
3=16/5(rej.) or 4x=1/5
(because no solution) or x=1/20
so x=1/20
(唔sure)
3)x^2 - |x| - 12 = 0
|x|^2 - |x| - 12 = 0
(|x|-4)(|x|+3)=0
(|x|-4)=0 or (|x|+3)=0
|x|=4 or |x|=-3(rej.)
x=+2 or -2

1)-1
2)sorry!! I don't know!!
3)sorry!! I don't know!!

1.-1
2.唔識

2007-12-13 21:38:34 補充：
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