(1)f'(x)=lim(Îxâ0)[(x+Îx)²-2(x+Îx)-(x²-2x)]/Îx =lim(Îxâ0)[2xÎx+Îx²-2Îx]/Îx =2x-2 â´f'(1)=0 (2)s=t²+3 s(2)=4+3=7 s(3)=9+3=12 â´Îs=s(3)-s(2)=5ï¼Ît=3-2=1 â´å¹³åé度=Îs/Ît=5 v=ds/dt=2t â´t=2ç§æ¶çç¬æ¶é度=4
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