已知(a+2b)的2次方=4分之1,(a-2b)的3次方=8分之27,求2[2(a+2b)的2次方-3(a-2b)的3次方]-3[(a+

2025-06-23 10:56:13
推荐回答(2个)
回答1:

解:已知设(a+2b)²=1/4=y,(a-2b)³=27/8=x
那么2<2y-3x>-3(y-5x/3)=2(1/2-81/8)-3(1/4-405/24)=-77/4+399/8=322/8=161/4

回答2:

1.a³+4a²b+4ab²
=a(a²+4ab+4b²)
=a(a+2b)²
2.2a²-b²/8
=1/8(16a²-b²)
=1/4(4a+b)(4a-b)
3.a²(x-y)+b²(y-x)
=a²(x-y)-b²(x-y)
=(a²-b²)(x-y)
=(a+b)(a-b)(x-y)