Question

已知X+Y=5，XY=3，求代数式X的3次方Y-2X的平方Y的平方+Xy的3次方的值

Answer 1

X的3次方Y-2X的平方Y的平方+Xy
=xy(x^2+y^2)-2x^2y^2
=xy[(x+y)^2-2x^2y^2]-2x^2y^2
=3(25-6)-2*9
=39

Answer 2

x³y-2x²y²+xy³
=xy(x²-2xy+y²)
=xy(x²+2xy+y²-4xy)
=xy[(x+y)²-4xy]
=3×(5²-4×3)
=3×13
=39