[plz help!!!]F.2數學題

1.) 化簡61-(3+2x)(3-2x)(4x^2+9)
=61-(9-4x^2)(4x^2+9)
=61+(4x^2-9)(4x^2+9)
=61+(16x^2-81)
=16x^2-20
2.) 因式分解-3(r-s)x-6(s-r)y
=3x(s-r)-6y(s-r)
=(s-r)(3x-6y)
=3(s-r)(x-2y)
3.) 因式分解? (2x+5)(x-3)
=2x^2+5x-6x-15
=2x^2-x-15
4.) 用加減消元法解聯立方程
╭7x+2y=9........(1)
╰ -x+4y=3........(2)
(1)x2-(2):
14x-(-x)=18-3
15x=15
x=1......(3)
將(3)代入(1):
7(1)+2y=9
2y=2
y=1
所以x=1,y=1

2007-12-30 14:48:04 補充：
3.) (2x+5)(x-3)你係唔係想化簡?

1) 61-(3+2x)(3-2x)(4x^2+9)
= 61 - (9 - 4x^2)(9 + 4x^2)
= 61 - 81 + 16x^4
= 16x^4 - 20
= 4(4x^4 - 5)

2) -3(r-s)x-6(s-r)y
= -3(r-s)(x + 2y)

3) (2x+5)(x-3)
= 2x^2 + 5x - 6x - 15
= 2x^2 - x -15
= (2x + 5)(x - 3)

4)╭7x+2y=9........(1)
╰ -x+4y=3........(2)

(1) X 2 ,
14x + 4y = 18 .....(3)
(3) - (2),
14x + 4y + x - 4y = 18 - 3
x = 1
將x = 1 放入(2)
-1 + 4y = 3
y = 1

因此,x=1,y=1