(1)原式=(a-1/2+a+1/2)(a-1/2-a-1/2)(a+3)
=-2a(a+3)
=-2×(-2)(-2+3)
=4(平方差公式)
(2)原式= (x-1/2y-1)³
=(1.5-0.45-1)³
=0.05³
=0.000125