ãåèçæ¡ã
15ãåå¼=(a/b)b²â(ab)Ã(-3a/2)âbÃ3â(a/b)
=abâ(ab)Ã(-9/2)aâa
=(-9a²b/2)â(a²b)
=-4.5a³bâb
16ãåå¼=[ây(âx-ây)/(x-y)]-â(xy)+[xây(âx-ây)/(x-y)]+â(xy)
=[(â(xy)-y)/(x-y)]+[(xâ(xy)-xy)/(x-y)]
=[(1+x)â(xy)-xy-y]/(x-y)
17ãa=â2
â2x-â2<2â2
â2x<3â2
x<3
â´x=1ã2
18ãâµâ³BCDæ¯çè¾¹ä¸è§å½¢ï¼â DBC=60°
â´â DBA=30°
â´BD=2AD=2â2
AB=â6
â´å¨é¿ä¸º2Ã2â2+â2+â6=5â2+â6
19ãâ åå¼=1+(1/2)-[1/(2+â5)]=3.5-â5
â¡â{1+[1/(n-1)²]+(1/n²)}
=1+[1/(n-1)]-[1/(n-1+n)]
=1+[1/(n-1)]-[1/(2n-1)]
=(2n²-2n+1)/(2n²-3n+1)
20ãæ¹æ³å¾å¤ï¼ä¸¾ä¾å¦ä¸ï¼
â å°6个æ£æ¹å½¢ææ1è¡æ1åï¼å¾å°é¿ä¸º12Ã6ã宽为12çé¿æ¹å½¢ï¼
对è§çº¿ä¸ºâ(72²+12²)=12â37cm
â¡å°6个æ£æ¹å½¢ææ2æï¼æ¯æ3个ï¼å¾å°é¿ä¸º12Ã3ã宽为12Ã3çé¿æ¹å½¢ï¼
对è§çº¿ä¸ºâ(36²Ã2)=36â2
11ãåå¼=8â6-18â6+12â6-10â6
=-8â6
12ãåå¼=-(â2-â3)²
=2â6-5
13ãåå¼=6Ã(1/2)÷5â2
=3÷5â2
=(3/5)Ã(â2/2)
=0.3â2
14ãåå¼=2bÃ(1/b)Ãâ(ab)+3Ãâ(ab)-4aÃ(1/a)â(ab)-3â(ab)
=2â(ab)+3â(ab)-4â(ab)-3â(ab)
=-2â(ab)æ¥èªï¼æ±å©å¾å°çåç
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