1.åç®(1-1/x-1)/(x/x^-1)å¨éæ©ä¸ä¸ªéå½çxæ±å¼
解(1-1/(x-1))/(x/(x^-1))
=((x-2)/(x-1))/(x/(x+1)(x-1))
=(x-2)/(x-1)*(x+1)(x-1)/x
=(x-2)(x+1)/x
å½x=2æ¶,åå¼=0
xéå½çå¼ä¸å®ä¸è½æ¯1,-1,0
2.ã1/2(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
3. 9x+6x^2 -3(x-2/3x^2).å
¶ä¸x=-2
9x+6x² -3(x-2/3x²)
=9x+6x²-3x+2x²
=8x²+6x
=8Ã(-2)²+6Ã(-2)
=32-12
=20
4. 9x+6x^2 -3(x-2/3x^2).å
¶ä¸x=-2
9x+6x² -3(x-2/3x²)
=9x+6x²-3x+2x²
=8x²+6x
=8Ã(-2)²+6Ã(-2)
=32-12
=20
5.1/4(-4x^2+2x-8)-(1/2x-1),å
¶ä¸x=1/2
1/4(-4x²+2x-8)-(1/2x-1)
=-x²+1/2x-2-1/2x+1
=-x²-1
=-(1/2)²-1
=-1/4-1
=-5/4
6. 3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz,å
¶ä¸x=-2,y=-3,z=1,
:3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz
=3x'y-2x'y+2xyz-x'z+4x'z-xyz
=x'y-xyz+3x'z
=4*(-3)-2*3*1+3*4*1
=-12-6+12
=-6
7. (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
8. 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
9. ã(X-2åä¹1Y-1)(X-2åä¹1Y+1)-(X-2åä¹1Y-1)çå¹³æ¹
å
¶ä¸X=1.7,Y=3.9(å
åç®åæ±å¼)
[(X-2åä¹1Y)-1][(X+2åä¹1Y)+1]-(X-2åä¹1Y-1)å¹³æ¹
=(X+2åä¹1Y)å¹³æ¹-1-(X-2åä¹1Y)å¹³æ¹+2(X-2åä¹1Y)-1
=(X+2åä¹1Y)å¹³æ¹-(X-2åä¹1Y)å¹³æ¹+2(X-2åä¹1Y)-2
=2XY+2X-Y-2
=3.9*2.4+1.4
=10.76
10. å
åç®åæ±å¼,1/2a-(2a-2/3b^2)+(-3/2a+2b^2)å
¶ä¸a=-2,b=2/3
åå¼=-3a+8/3b^2
å½a=-2,b=2/3æ¶,
åå¼=6+8/3Ã(4/9)=194/27
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