å享ä¸ç§è§£æ³ãç±é¢è®¾æ¡ä»¶ï¼æ∂x/∂t=1/(1+t²)ï¼∂y/∂t=[â(1+2t²)]/(1+t²)ï¼tanx=tã
â´[(∂x/∂t)²+(∂y/∂t)²]^(1/2)=(â2)/â(1+t²)ã
â´åå¼=â«(0,1)t{[(∂x/∂t)²+(∂y/∂t)²]^(1/2)}dt=(â2)â«(0,1)tdt/â(1+t²)=(â2)â(1+t²)丨(t=0,1)=2-â2ã
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