八下數(shù)學(xué)題目（1/x-y+1/x+y)÷x2y/x2-y2=(x+y+x-y)/(x2-y2)*(x2-y2)/x2y=2/xy其中x=根號(hào)3+1,y=根號(hào)3-1,原式=2/(√3+1)(√3-1)=2/2=12，八下數(shù)學(xué)題目設(shè)一共進(jìn)購了x支筆(a+2)x=399a+805,則x=（399a+805）/(a+2)，x=399+7/(a+2)又因?yàn)閍為整數(shù)所以a為5設(shè)一共進(jìn)購了x支筆(a+2)x=399a+805x=（399a+805）/(a+2)x=399+7/(a+2)a為整數(shù)a為53，八年級(jí)下數(shù)學(xué)...