~數學~急~

1. (r+s)^2 - 5^2
(r+s+5)(r+s-5)

3. a^2 - 9^2
(a+9)(a-9)

4. 3^2x = 3^4
2x=4
x=2

6. (3x)^2 - 2.3x.2y + (2y)^2 -(2z + 1)^2
(3x-2y)^2 -(2z+1)^2
(3x-2y+2z+1)(3x-2y-2z-1)

2007-10-28 21:41:02 補充：
2. r (r^2 - 12r -45) = r (r ^2 -2.6r 6^2 -81) = r [ ( r-6)^2 - 9^2 ] = r( r-6 9) (r-6-9)=r(r 3) (r-15)

1. r^2+2rs+s^2-25 = (r+s)^2-5^2 = (r+s-5)(r+s+5)

2. r^3-12r^2-45r= r(r^2-12r-45) = r(r-15)(r+3)

3. a^2-81= a^2-9^2 = a-9)(a+9)

4. 3^2x=81
3^2x=3^4
2x=4
x=2

6. 9x^2-12xy+4y^2-1-4z-4z^2
=(3x-2y)^2-(2z+1)^2
=(3x-2y-2z-1)(3x-2y+2z+1)

7.4x^2+2xy-6y^2
= 4(x^2+xy/2+y^2/16-y^2/16)-6y^2
= 4(x+1/4)^2-(25y^2)/4
= (2x+1/2-5y/2)(2x+1/2+5y/2)