4、______⑤(-10)×(-)×(-0.1)×(-6)×0=__________比较上面几个式子:当因数中有______个负数时,积为正;当因数中有______个负数时,积为负。几个不为零的数相乘,首先______________,然后_______________。几个数相乘,有一个因数为零,____________________________。例2、计算:①(-5)×(-)×3×(-2)×2 ② (-)×8×(-)×(-)=_______(5××3×2×2)=-=______________=______________③(-)×5×0×