若x+y=3,xy=5则求x方-xy-y方,x立方+y立方的值
问题描述:
若x+y=3,xy=5则求x方-xy-y方,x立方+y立方的值
答
x^2-xy-y^2=(x-y)^2+xy=3^2+5=14
x^3+y^3=(x+y)(x^2-xy+y^2)=3*14=42