... = - - + = = 31 3 3 9 0 ,25 ( ) ( ( ) ) e I = I1 + 3I = IV (1im) -2 + 2e3 0 ,25 S K H B I C A uu r uuu r *Tacú IA = -2 ị HthuctiaicatiaIAv IA =2 IH IH BC = AB =2 Suyra IA = a ,IH = a a ị AH = IA ... a = = ị d ( K , ( SAH ) ) = d ( B,( SAH ) )= BI = SB 2 2 2 V Doa,b,c>0v a + b + c =1 nờn a, b, c ẻ( 01 ) (1im) 2 a - + a a a - a Tacú = = - a + a 2 b +c 1 -a ( ) 0 ,25 0,5 3 3 Btngthctrthnh - a ... + IH = a 0 ,25 a 2 Tacú HC = AC + AH - AC AH cos 45 ị HC = ( Vỡ SH ^ ( ABC ) ị SC , ( ABC ) 0 ,25 a 15 = éSCH = 60 ị SH = HC tan 60 = ) a 2 Tacú HC = AC + AH - AC AH cos 45 ị HC = a 15 Vỡ...