奧數有幾題唔識做...

1. let father aged x , and son aged y ,

then x=5y and (x+18)=2(y+18)

=>x=5y and x=2y+18

=>5y=2y+18

=>3y=18 =>y=6 and x=5y=5*6=30//

2. let the date of that satuaday is x and as we know , one month has 4 weeks ,

then the dates are x , x+7 ,x+14 , x+28

=>x+x+7+x+14+x+21 = 54

=>4x+42=54

=>x=3 //



2010-02-05 23:14:37 補充：
4. x^3-1/x^3

=(x-1/x)[x^2+(x)(x/x)+(1/x)^2]

=x^2+1+1/x^2

=x^2-2+1/x^2+3

=x^2-2(x)(1/x)+(1/x)^2+3

=(x-1/x)^2+3

=1+3

=4//