(+1)*(+2)*...*(+202)*(+203)*(-1/203)*(-1/202)*...*(-1/2)*(-1)
= (+1)*(-1)*(+2)*(-1/2)*...*(+202)*(-1/202)*(+203)*(-1/203) 【乘法交换律】
= [(+1)*(-1)]*[(+2)*(-1/2)]*...*[(+202)*(-1/202)]*[(+203)*(-1/203)] 【乘法结合律】
= (-1)*(-1)*...*(-1)*(-1) 【共203个(-1)】
= -1