3ã设f(xï¼yï¼z)=âx+ây+âz-2ï¼
f 对 xãyãz çå导æ°åå«ä¸º
fx'=1/2âxï¼fy'=1/2âyï¼fz'=1/2âzï¼
设(x0ï¼y0ï¼z0)æ¯æ²é¢ä¸ä»»ä¸ç¹ï¼
ååå¹³é¢æ¹ç¨ä¸º 1/2âx0(x-x0)
+1/2ây0(y-y0)+1/2âz0(z-z0)=0ï¼
注æå° âx0+ây0+âz0=2ï¼åå¹³é¢æ¹ç¨å¯å为 x/(2âx0)+y/(2ây0)+z/(2âz0)=1ï¼
æ以ä¸ä¸ªæªè·ä¹å为
2âx0+2ây0+2âz0=2*2=4 ã
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