about mathematics....

1) (3x+2) (2-5x)
= 3x (2-5x) +2 (2-5x)
= 6x -15x* +4 -10x
= 4 -4x -15x*

2) 5x(x-3)(x-4) -2x* (x-3)
= (5x* - 15x) (x-4) - 2x" + 6x
= 5x* (x-4) -15x (x-4) - 2x" +6x
= 5x" - 20x* - 15x* + 60x - 2x" +6x
= 3x" - 35x* + 66x

3) (x+y)* - (x-y)*
= (x*+ 2xy + y*) - ( x* - 2xy + y*)
= x* +2xy + y* - x* +2xy - y*
= 4xy

P.S.
* = 2次方
" = 3次方

希望幫到你~~

1)-15x^2-4x+4 it needs only one step
2) 2x * means 2x^2 or (2x)^2?
5x(x^2-7x+12)-2x^3+6x^2
=5x^3-35x^2+60x-2x^3+6x^2
=3x^3-29x^2+60x
3) (x+y)^2-(x-y)^2
by a^2-b^2=(a+b)(a-b)
(x+y+x-y)(x+y-x+y)
=4xy

2007-08-08 21:59:35 補充：
^ means to the power by any calculatorsYou can try by yourself