å½æ°fï¼xï¼=x^2-2x+kãkâRï¼å½a+bâ¤2æ¶ï¼å¨å®ä¹å[aï¼b]å
ï¼å¼åä¹æ¯[aï¼b]ï¼æ±å®æ°kçåå¼èå´ã
解æï¼âµå½æ°f(x)=x^2-2x+kãkâRï¼å½a+bâ¤2æ¶ï¼å¨å®ä¹å[a,b]å
ï¼å¼åä¹æ¯[a,b]
â´a<=b
b<=2-a==>a<=2-a
â´a<=1==>-a>=-1==>b>=1
â´a<=1<=b<=2-a
âµå½æ°f(x)为å¼å£åä¸çæç©çº¿ï¼å¯¹ç§°è½´ä¸ºx=1æå°å¼ä¸ºf(1)=k-1
â´å½xâ¥1æ¶f(x)为å¢å½æ°ï¼x<1æ¶f(x)为åå½æ°ï¼
k-1=a==>k=a+1
f(x)å¨åºé´[a,b]ä¸çæ大å¼ä¸ºf(a)ï¼f(b)è¾å¤§è
âµa+bâ¤2==>(a+b)/2â¤1
â´f(a)ï¼f(b)è¾å¤§è
为f(a)
â´f(a)=b==> f(a)=a^2-2a+k=b
代å
¥kå¾f(a)=a^2-a+1=b
å³f(a)=a^2-a+1>=1
â´å½aâ¤0ï¼bâ¥1æ¶k=a+1
å½a<1ï¼b<1æ¶
æç¥f(x)å¨åºé´[a,b]ä¸åè°éåï¼åf(a)=bï¼f(b)=a
å³a^2-2a+k=bï¼b^2-2b+k=a
两å¼ç¸åå¾a+b=1
两å¼ç¸å å¾k=[3(a+b)-(a^2+b^2)]/2=[3-(a^2+b^2)]/2
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