X+Y=3,XY=1求X的三次方乘以Y+X乘以Y的三次方

X+Y=3,XY=1求X的三次方乘以Y+X乘以Y的三次方
X+Y=3,XY=1求X的三次方乘以Y+X乘以Y的三次方

X+Y=3,XY=1求X的三次方乘以Y+X乘以Y的三次方
x^3y+xy^3
=xy(x^2+y^2)
=xy[(x+y)^2-2xy]
=1*(9-2)
=7

3 乘法结合律

X+Y=3
XY=1
X^2+Y^2=(X+Y)^2-2XY=3^2-2*1=7
XY^3+XY^3=XY(X^2+Y^2) =1*7=7

X的三次方乘以Y+X乘以Y的三次方=（X的三次方乘以Y的三次方）乘以Y+X
=（XY）的三次方乘以Y+X
=X+Y=3