æ±ä¸åå½æ°çæå¼
(4). y=x+â(1-x)
解ï¼å®ä¹åï¼1-xâ§0ï¼å³xâ¦1;
令y'=1-1/[2â(1-x)]=0ï¼å¾ 2â(1-x)=1ï¼å³æ1-x=1/4ï¼æ
å¾é©»ç¹x=3/4;
å½x<3/4æ¶y'<0ï¼å½x>3/4æ¶y'>0ï¼æ
x=3/4æ¶æ大ç¹ï¼
æ大å¼y=y(3/4)=3/4+â(1/4)=3/4+(1/2)=5/4;
(6). y=(e^x)cosx
解ï¼ä»¤y'=(e^x)cosx-(e^x)sinx=(e^x)(cosx-sinx)=0
âµe^x>0对任ä½xé½æç«ï¼æ
å¿
æ cosx-sinx=0ï¼æ
å¾é©»ç¹ x=Ï/4ï¼
x<Ï/4æ¶y'>0ï¼x>Ï/4æ¶y'<0ï¼æ
x=Ï/4æ¯æå°ç¹ï¼
æå°å¼y=y(Ï/4)=[e^(Ï/4)](â2/2)=[(â2)e^(Ï/4)]/2;
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