Maths~

5a. f(2)=2*2=4
g(2)=2^2=4
5b.
g(f(x))-f(g(x))=16
g(2x)-f(x^2)=16
(2x)^2-2*(x^2)=16
4x^2-2x^2=16
2x^2=16
x^2=8
x=sqrt(8)=2sqrt(2)=2.8284271247461900976033774484194

6ai.
Let x=0.2020202020..................
100x=20.20202020.............
100x-x=20.20202020..........................-0.2020202020...............
99x=20
x=20/99


6aii.
Let x=0.505050505050.........
100x=50.505050505050........
100x-x=50.5050505050.............-0.505050505050...............
99x=50
x=50/99

6b.
20x/99+6=(2+50/99)x
20x/99+6=(248/99)x
6=228x/99
x=99/38

31a.
Let x=0.0025252525..............
100x=0.25252525......
100x-x=0.25252525...........-0.0025252525.............
99x=0.25
x=0.25/99=1/396

31b.
0.2225252525.............=0.22+0.00252525............=22/100+1/396=2203/9900

51a.
(x-7)(x+2)=14-5x-12
x^2-5x-14=14-5x-12
x^2=14-12+14
x^2=28-12
x^2=14
x=+sqrt(14) or -sqrt(14)

51b
5(x-7)(x+2)+x(14-5x)=7
5(x^2-5x-14)+x(14-5x)=7
5x^2-25x-70+14x-5x^2=7
-11x-70=7
-11x=77
x=-7

我答問題好慢ka, 不過好肯定啱至post嘅:
http://s238.photobucket.com/albums/ff245/chocolate328154/?action=view¤t=Maths321.jpg