a的3次方-4ab的平方/a的3次方-4a的平方b+4ab的平方
=(a³-4ab²)/(a³-4a²b+4ab²)
=a(a²-4b²)/a(a²-4ab+4b²)
=(a-2b)(a+2b)/(a-2b)²
=(a+2b)/(a-2b) a=-2,b=-0.5
=[-2+2*(-0.5)]/[-2-2(-0.5)]
=(-2-1)/(-2+1)
=(-3)/(-1)
=3