选择适当的公式计算:(1)(-a+3)(a-3) (2)(-a-3)(a-3)

问题描述:

选择适当的公式计算:(1)(-a+3)(a-3) (2)(-a-3)(a-3)

解1(1)(-a+3)(a-3)
=-(a-3)(a-3)
=-(a-3)²
=-(a²-6a+9)
=-a²+6a-9
(-a-3)(a-3)
=-(a+3)(a-3)
=-(a²-9)
=9-a²