幫我計因式分解ar thx~有20分

1) 4a²(y-2)²-a²
= [2a(y-2)]²-a²
= [2a(y-2)+a][2a(y-2)-a]
= a²(2y-4+1)(2y-4-1)
= a²(2y-3)(2y-5)


2) 9a²-4b²-9a-6b
= (3a)²-(2b)²-9a-6b
= (3a+2b)(3a-2b)-3(3a+2b)
= (3a+2b)(3a-2b-3)


3) x²+14x-15
= (x+15)(x-1)


4) -2px-qx+2py+qy+3ry-3rx (同你寫ga題目唔同,因為我覺得你可能寫錯左)
= 2p(y-x)+q(y-x)+3r(y-x)
= (2p+q+3r)(y-x)


5) y²-x²-2xy-2y²
= -y²-x²-2xy
= -(y²+x²+2xy)
= -(y+x)²


6) 25(3x-2y)²-9(2x+y)²
= [5(3x-2y)]²-[3(2x+y)]²
= [(15x-10y)+(6x+3y)][(15x-10y)-(6x+3y)]
= (21x-7y)(9x-13y)
= 7(3x-y)(9x-13y)


7) (a²+b²)²-4a²b²
= (a²+b²)²-(2ab)²
= (a²+b²+2ab)(a²+b²-2ab)
= (a+b)²(a-b)²


8) 12(c²+2)-2(c²+2)²-18(我都係覺得你寫錯題目)
= -[2(c²+2)-6][(c²+2)-3]
= -(2c²+4-6)(c²-1)
= -(2c²-2)(c²-1)
= -2(c²-1)²
= -2(c+1)²(c-1)²

2008-08-23 20:03:51 補充：
心得
做以上題目ga時候,大部份人都會著眼係2個有相同代數ga項上面,其實解e類數最重要係消去指數,因為這類數最重要的代數多數都會帶有指數的。