Video h ng d n k thu t casio gi i nhanh có t i FB th y: Tr n Hoài Thanh K THU T CASIO GI I BÀI TOÁN C C TR S PH C S u t m : Tr n Hoài Thanh ậTHPT Khúc Th a D , Ninh Giang, H i D ng https://www.facebook.com/tranhoaithanhvicko FB: H C CASIO FREE T I: https://tinyurl.com/casiotracnghiem Group: TH THU T CASIO THPT https://fb.com/groups/casiotracnghiem I) KI N TH C N N T NG B ng th ng g p  B ng th c Bunhiacopxki :Cho s th c a , b, x, y ta ln có  ax  by  B   a  b2  x2  y2  D u = x y  ng th c V : Cho vecto u  x; y a b  x y