注æå°
â«[0,1] f(x)dxæ¯ä¸ä¸ªå®å¼ï¼è®¾â«[0,1] f(x)dx=B
â«[0,2] f(x)dxæ¯ä¸ä¸ªå®å¼ï¼è®¾â«[0,2] f(x)dx=A
f(x)=x^2-Ax+2B
两边æ±å®ç§¯åå¾
B=â«[0,1] f(x)dx
=â«[0,1] (x^2-Ax+2B)dx
=(x^3/3-Ax^2/2+2Bx)[0,1]
=1/3-A/2+2B
=B
å³
1/3-A/2+B=0 (1)
A=â«[0,2] f(x)dx
=â«[0,2] (x^2-Ax+2B)dx
=(x^3/3-Ax^2/2+2Bx)[0,2]
=8/3-2A+4B
8/3-3A+4B=0 (2)
(1)(2)解å¾
A=4/3,B=1/3
f(x)=x^2-4/3x+2/3
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