二條超簡單的數

1)
(20+2x)(15+2x)-(20*15)=246
300+70x+4x^2-546=0
4x^2+70x-246=0
(2x+41)(2x-6)=0
x=-41/2 or x=3

2)
3x(x-12)=0
x=0 or x=12

(ax+b)(cx+d)......(kx+n)=0
There must be at least one binomials ax+b,cx+d......kx+n is equal to 0
Therefore ax+b=0 or cx+d=0...... or kx+n=0
x=-b/a or x=-d/c ...... or x=-n/k

1. (20+2x)(15+2x)-(20*15)=246
2x(20+15)-(300)=246
2x(35)=246+300
2x=546/35
x=15.6/2
x=7.8

2. 3x(X-12)=0
3x(x)-3x(12)=0
3x^2-36x=0
3x^2=36x
x^2 / x =36/3
x=12

2006-10-22 16:08:45 補充：
^係二次方既意思~!

1. 300+30x+40x + 4x^2-300=246
4x^2+70x-246=0
2x^2+35x-123=0
(2x+41)(x-3)=0
x=-20.5 or x =3

2. x=0 or x=12