1.ï¼3X+2Y)+(4X+3Y)å
¶ä¸X=5,Y+3
åå¼=3X+2Y+4X+3Y=7X+5Y
å½X=5,Y=3æ¶
åå¼=5*7+ï¼-3ï¼*5+20
2.(5a^2-3b^2)+(a^2+b^2)-(5a^2+3b^2),å
¶ä¸a=-1,b=1
=5a^2-3b^2+a^2+b^2-5a^2-3b^2
=a^2-5b^2
=(-1)^2-5*1^2
=1-5
=-4
3.2(a^2b+ab^2)-2(a^2 b-1)-2ab^2 -2å
¶ä¸a=-2,b=2
=2a^2b+2ab^2-2a^2b+2-2ab^2-2
=0
1ãå·²ç¥A,Bæ¯æ¹ç¨x^2+2x-5=0ç两个å®æ°æ ¹,
æ±(A^2+2AB+2A)(B^2+2AB+2B)çå¼.
ç±A,Bæ¯æ¹ç¨x^2+2x-5=0ç两个å®æ°æ ¹å¾ï¼
AB=-5,A+B=-2
A^2+2AB+2A)(B^2+2AB+2B)
=ABï¼A+2B+2ï¼ï¼B+2A+2ï¼
=-5ï¼-2+B+2ï¼ï¼-2+A+2ï¼
=-5AB
=25
2ã1/2(x+y+z)æ¹+1/2(x-y-z)(x-y+z)-z(x+y),å
¶ä¸x-y=6,xy=21.è¦è¯¦ç»æ¥éª¤
åç®å¾ï¼
1/2(x+y+z)æ¹+1/2(x-y-z)(x-y+z)-z(x+y)=
1/2[(x+y)æ¹+2z(x+y)+zæ¹]+1/2[(x-y)æ¹-zæ¹]-z(x+y)=
1/2(x+y)æ¹+1/2(x-y)æ¹=xæ¹ï¼yæ¹
ç±x-y=6,xy=21å¾,xæ¹ï¼yæ¹ï¼ï¼x-yï¼æ¹ï¼2xyï¼78
3ãa^2-ab+2b^2=3 æ±2ab-2a^2-4b^2-7çå¼
2ab-2a^2-4b^2-7
=2(ab-a^2-2b^2)-7
=-2(a^2-ab+2b^2)-7
=(-2)*3-7
=-6-7=-13
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