已知x+y=3,xy=-12,求x²+y²与x²-xy+y²的值.

已知x+y=3,xy=-12,求x²+y²与x²-xy+y²的值.
已知x+y=3,xy=-12,求x²+y²与x²-xy+y²的值.

已知x+y=3,xy=-12,求x²+y²与x²-xy+y²的值.
x²+y²
=(x+y)²-2xy
=3²-2*(-12)
=9+24
=33
x²-xy+y²
=x²+2xy+y²-3xy
=(x+y)²-3xy
=3²-3*(-12)
=9+36
=45

x+y=3,xy=-12

x²+y²=（x+y）²-2xy
=9+24
=33

x²-xy+y²
=x²+y²-xy
=33+12
=45

x²+y²=（x+y）²-2xy=9+24=33
x²-xy+y²=(x+y)²-3xy=9+36=45