éè¿ååãåé¨ç§¯åãæ¢å çå®ç§¯å计ç®æ¹æ³ï¼ä»ç»æ±è§£å®ç§¯åâ«[0,3](x+2)dx/â(x+1)çå¼ä¸»è¦æ¥éª¤åæ¹æ³ã
â«[0,3](x+2)dx/â(x+1)
=â«[0,3](x+2)d(x+1)/â(x+1),æ¬æ¥éª¤å ¬å¼:d(x+1)=1dx.
=2â«[0,3](x+2)d(x+1)/2â(x+1),æ¬æ¥éª¤ä¸ºååæ³.
=2â«[0,3](x+2)dâ(x+1)
=2â«[0,3]xdâ(x+1)+4â«[0,3]dâ(x+1)ï¼å°ç§¯åé¨åå项å¾å°.
=2xâ(x+1)[0,3]-2â«[0,3]â(x+1)dx+4â(x+1)[0,3]
=2*6-2â«[0,3]â(x+1)d(x+1)+4(2-1).
=2*6-4/3â(x+1)^3[0,3]+4(2-1).
=20/3.
设â(x+1)=tï¼åx=(t^2-1),åï¼
å½x=0æ¶ï¼t=1ï¼å½x=3æ¶ï¼t=2ï¼æ¤æ¶æï¼
â«[0,3](x+2)dx/â(x+1)
=â«[1,2][(t^2-1)+1]d[(t^2-1)]/t
=2â«[1,2][(t^2-1)+2]dt
=2â«[1,2](t^2+1)dt
=2(1/3t^3+t)[1,2]
=2[1/3(2^3-1^3)+1(2-1)]
=20/3.
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â«(a,b)[f(x)±g(x)]dx=â«(a,b)f(x)±â«(a,b)g(x)dx
â«(a,b)kf(x)dx=kâ«(a,b)f(x)dxã