1、1已知x+y-5,xy6,则x2+y2的值是 ( ) A1 B13 C17 D252已知:a-b=3,ab=1,则a2-3ab+b2=_3若a+b=4,则a2+2ab+b2的值为_4.1022等于 ;5.计算:982+(a-b)26已知:x+y=6,xy=4(1)求x2+y2的值;(2)求(x-y)2的值;(3)求x4+y4的值7若x2+y2=86,xy=-16,求(x-y)28知(m+n)2=10,(m-n)2=2,求m4+n4的值9计算:29.830.2;46512;2052答案:1B 28 3.16 4.104045.解:982+(a-b)2=(100-2)2+a2+2ab2+b2=10
2、000-400+4+a2+2ab2+b2=9604+a2+2ab2+b26解:x+y=6,xy=4,(1)x2+y2=(x+y)2-2xy=62-24=28; (2)(x-y)2=x2+y2-2xy=28-24=20; (3)x4+y4=(x2+y2)2-2x2y2=(x2+y2)2-2(xy)2=202-242=3687解:(x-y)2=x2+y2-2xy,且x2+y2=86,xy=-16,(x-y)2=86-2(-16)=1188解:(m+n)2=10,(m-n)2=2,m2+2mn+n2=10,m2-2mn+n2=2,相减得:4mn=8,2mn=4,m4+n4=(m2+n2)2-2(mn)2=(m+n)2-2mn2-8=10-42-8=36-8=289解:29.830.2=(30+0.2)(30-0.2)=302-0.22=900-0.04=899.96;46512=212512=(25)12=1012;2052=(200+5)2=40000+2000+25=42025