已知x+y=a,x2+y2=b2,求x4+y4的值.
问题描述:
已知x+y=a,x2+y2=b2,求x4+y4的值.
答
∵x+y=a
∴x2+y2+2xy=a2
又∵x2+y2=b2
∴2xy=a2-b2
x4+y4=(x2+y2)2-2x2y2=(x2+y2)2-
=b4−(2xy)2 2
=-(a2−b2)2 2
a4+a2b2+1 2
b4.1 2