(ii)当直线y??3x?1与⊙E相切时,如图所示. 33x?1与⊙E相切时的切点, 3则符合题意的点N是直线y??记直线y??3x?1与x轴交于点R(3,0), 3若点E在点R的左侧,
由E1N1?2,可得RE1?4,OE1?4?3, ∴t1??4?3. 若点E在点R的右侧,
由E2N2?2,可得RE2?4,OE2?4?3. ∴t2?4?3. (iii)当直线y??3x?1与⊙E相交时, 3?4?3 综上,t的取值范围是:?4?3≤t≤4?3. y6y=-33x+14N12-5E1O5N2E2xy=-33x+1y=-3x+1 R-2 17
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