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化简求值:x?yx+2y÷x2?y2x2+4xy+4y2%2,其中x=1+2...

x?yx?2y÷x2?y2x2?4xy+4y2=x?yx?2y?(x?2y)2(x+y)(x?y)=x?2yx+y;当x=1+2,y=1-2时,原式=1+2?2(1?2)1+2+1?2=3

x?yx+2y÷x2?y2x2+4xy+4y2-1=x?yx+2y×(x+2y)2(x?y)(x+y)?1=x+2yx+y?1=yx+y故答案为:yx+y

(1)原式=1-x?yx?2y?(x?2y)2(x?y)(x+y)=1-x?2yx+y=x+y?x+2yx+y=3yx+y,当x=2,y=5时,原式=3×52+5=157;(2)原式=(x+2)(x?2)+4(x?2)2?x?2x=x2(x?2)2?x?2x=xx?2,当x=-12时,原式=?12?12?2=15.

原式=1-x?yx+2y×(x+2y)2(x+y)(x?y)=1-x+2yx+y=-yx+y.故答案为:-yx+y.

(1)原式=a6b38c3?(-c2ab)?a2bc2=-a7b8c3;(2)原式=4-(x+2)2(x+2)(x-2)=-(x-2)2(x+2)(x-2)=-12(x+2);(3)原式=1-x-yx+2y?(x+2y)2(x+y)(x-y)=1-x+2yx+y=x+y-x-2yx+y=-yx+y;(4)原式=x-3x-2÷(x+2)(x-2)-5x-2=x-3x-2?x-2(x+3)(x-3)=1x+3.

(1)∵x2-4x-1=0,∴x2-4x=1,原式=4x2-12x+9-(x2-y2)-y2=3x2-12x+9=3(x2-4x)+9=3×1+9=12;(2)原式=x+2yx+y?xyx+2y÷x+yxy=x+2yx+y?xyx+2y?xyx+y=x2y2(x+y)2当x=-2,y=3时,原式=36.

原式=x+2yx+y?xyx+2y÷x+yxy=x+2yx+y?xyx+2y?xyx+y=x2y2(x+y)2.

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