已知x-y=2,xy=-½,求x²+y²的值.

已知x-y=2,xy=-½,求x²+y²的值.
已知x-y=2,xy=-½,求x²+y²的值.

已知x-y=2,xy=-½,求x²+y²的值.
x²＋y²
=(x²－2xy＋y²)＋2xy
=(x－y)²＋2xy
=(2)²＋2×(－1/2)
=4－1
=3

x²+y²
=(x-y)²+2xy
=2²+2*（-1/2）
=4-1
=3

x²+y²=x²+y²-2xy+2xy=(x-y)²+2xy=4-1=3

=（x-y）²+2xy=4+（-1）=3