NGHÖ AN       DIÓN CHAU !"#$ %"pht ( không k thi gian giao đ) &' ()$"      x x − ≥ − −       x x+ − −  ≤ ()" !"#$%$&'%%()!*+,-!! .'%     /  0 1 2 3 )45      2   1  )%5567%58#9: ()*"  );<= α > / π + α =   6?   π α < <  @A"'B    !C  C x A − = − ()+" ! ABC∆ DD<=0  < =%<E=2%);F  .8G$HE  I9;J ABC ∆  .8G$KL+ b m G *!M'%<+E ()," !KN d COL>=6$'%PQO  );&!M'%P+KN d  R+KN,P6$6(D6?KN d  R++L+6?KS  ( ) ( )     3x y− + − = +T+L+D !!6?KN d ()-" B%T!%<E D ! ! !  /      A B C c A c B c C+ + − =  (Cn b coi thi không gii thch g thêm) ./0123"44444444444444444444444444444444444444444444444444456789:3;44444444444444444444444444444444444444444444  %<$='>?&>@ () AB9)3C BDE      x x − ≥ − −         x x x − + ⇔ ≥ − − Q.UVC=      x x x − + − − ECWGVC C −∞     +∞ OC> >X>X>O CO OXO>X> CO O>X>X> VC >XXOXX>O RYL9%J#$   O Q Q Z  S = ∞ ∪   ×        x x+ − − ≤  .UVC=     x x+ − − QVC=   x x =  ⇔  = −  ECWGVC C  −∞  −  +∞ VC >O> RYL9%J#$ [Q ZS = −   ×    \5     / 2 0 1 21 3  x + + + + + + + + + = =020 \567R54]JG^L#$5_`567#$8J5B a67;bG^L67;   6$   > 1 1 1  e M + ⇒ = = P5.'%2D45#?#$1  2M⇒ = c             020  020  020  020 / 020 2 020 0 020 1 020 12 020 3 020  x S − + − + − + − + − + − + − + − + − + − =  x S ≈ / .8#9:  x x S S= ≈      ×    )D   !  c α α = − =    / / − =  !  c α ⇒ = ± 6   π α < < ` !  α > RYL  !  c α = ⇒    ! c α α α = =     /   A π α α α + = + = − L    α = -         A + = − =     + −    ×        !C  C x A − = − =     !  !C  C x c x x+ − − =   !  !C C c x x− − =  !   !C>C !C  C c x x c− − = !C>Cc   /       !0a b c bc c= + − =     2 2  + − =/3 /3 1BC a⇒ = = = %   /      ABC S b c A ∆ = =   2   =   %    ×  /       / b a c b m + − = =    1 2   / + − =  13 b m⇒ = ≈ %  ×  /G *!M<+E T a h    1 ABC a S h a ∆ = = ≈ /3%    ( )           d M d − − + = + − =   ×   " ∆ #$KN,P6$6(D6?G )D d COL>= Q  d n⇒ = − uur R d∆ ⊥ ` ∆ DR) c u ∆ uur = Q  d n = − uur c%5J ∆      x t y t = +   = − −     )D  ( ) ( )     3x y− + − = ⇒ d%eQQ&;@= " l #$+L+JKS6 ffl d ` l DGHCOL>%= l +CA6?  e d l R⇒ =  ⇔         m− + = + −   m⇔ + =        m m  = − ⇔  = − −   RYLD+L+g%^L`4h$               l x y l x y − + − = − − − =     0 )!%<E D A B C π + + =    A B C π + ⇒ = −  ⇒  !    A B C+   =  ÷    R)= ! ! ! c A c B c C + + − = !  !   A B A B c + −      ÷  ÷         C − =  ! !    C A B A B c  − +      −  ÷  ÷         =        C A B    − −  ÷       = /      A B C =Rc%   ×   ijklIml inP fl+"D&%$6oA6$p-6?8G% &!6o!J'%M4,L7 f.'%J$&'%#$q'%J!$$6$#$%S+R;Gr0#$%S$0Q 01#$%S$1 . NGHÖ AN       DIÓN CHAU !"#$ %"pht ( không k thi gian giao đ) &' ()$"  