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-PA PB PC PD=  X c!dSef ,= AMBC 0+6*1I GM GA GB GC × = ×  /0 123/45 )% C- X c!d,= BFEC 0+6*1I GB GC GF GE× = × C- X ^* GF GE GM GA× = × C- X _,1"6= AMFE 0+- C- 670 N '/ 8 BC 4 H '9 :  ABC &'( ') ;+<25 =>'6?6 GH AN⊥ X g,H+JO6$)=`hPi0+* M > 12312H# AH 6 !,1" HM MA⊥ - C- X * MH :';123 4 5O ; K 6H1"!, VCAMK∠ = o   AK ')12H#G* 4 5O - C- X W1"* 6KC CA KB BA⊥ ⊥ -^* ]] 6 ]]KC BH KB CH 6!,1" BHCK ')7)- ^* KH 1J* N C- X [1" 6 6M H N 9)- C- X ,* GAN "*12*, 6AD NM :*; 6H   H ')@AG**  GAN -^* GH AN⊥ C- %&0'(')*+, ' N D K M G F E H O B C A D+=&4E2FG45:HI +,- a19=O=1$% ( )  B B     4 54 54 5  a b b c c a a b c abc a b b c c a abc   + + + + + + ≥ + + +  ÷ + + +   C- .=    4 54 54 5 4 5 4 5 4 5 a b b c c a c a b a b c b c a abc+ + + = + + + + + + C- c!d719=.*Xa*,HX^j*k ( ) ( )    B  B  B     4 5 4 5 4 5       - - -  -  c a b a b c b c a abc a b b c c a abc c a b a b c b c a abc a b b c c a abc c a b abc   + + + + + + + + + ≥  ÷ + + +     ≥ + + + + + +  ÷  ÷ + + +   = + + + _lmne*H$)MH  4 5 4 5 4 5  -c a b a b c b c a abc abc a b c+ = + = + = ⇔ = = C- C- %&)'('*+, D+=&4E2FG45:HI +,- X  &$E,6H#%  × M"HEJ*+,6o$S6" HEJ*+,B C- X pH#77q$E6H#%  × 6"R*+,6"R *+,B-_,1"6"#C3';HE*+,6oHE* +,B-Q$S6r')0,66N- X W1"6g, '\_'g6"0e#N'O- C- 4;0 1    )% ;+<25 =>'@?6 . ,* GAN "*12*, 6AD NM :*; 6H   H ')@AG**  GAN -^* GH AN C- %&0'(')*+, ' N D K M G F E H O B C A D+ =&4E2FG45:HI. ') 5J4KL2.,=`a._6b')*,1<G*`a$)._-=`a._0+ H$)MH - -PA PB PC PD=  X c !d Sef ,= AMBC 0+6*1I GM GA GB GC × = ×  /0 123/45 )% C- X c !d ,= BFEC 0+6*1I GB.  .,  *    /  ABC  0  +  12  3  4 O 5-  6 6AD BE CF ')  7*  12  *, ( ) 6 6D BC E CA F AB∈ ∈ ∈ -829 EF : BC ; 6G 129 AG :';123 4