... cosl20°=-o^ a AB 2x -21 Vx^+13.V38 = — = x< ^21 x< — 2( 2x -21 )2 =19(x^+13) 21 o x= llx2+168x-635 = -84 ± V14041 11 o ( n + 2) 2 -64(n + 2) -21 1 = n +2 = n +2 = 32 + V T 32- 3 723 1 22 + 3N /23 T ... a )2 + y2 + = « (X lE^ = I S ' ^ ^2 ^ y2 ^ _ 2a )2 - a )2 + (y - a )2 + z2 = x2 + y2 4- (2 - laf ,, I C t y TNHH MTV DVVII pgn A ' B , A ' D =(ab;ab;a2) =>A'M.rA'B,A'D Khang Vigt Sa^b x^+(y-a )2+ z2=x2+y2+(z_2a )2 ... (-3 )2 + (n + 2) ^ + a = (2; 3;l), b = (-3; -2; 0), c = (x ;2; -3) 1) Tim X de a A b vuong goc voi c 2( n + 2) + 16 2( n + 2) + 16n2 = (n + 2) 2+5 m-3 = 2) Tim X de goc giua hai vec to a A b va c bang 120 "...