1) Trong mat phang toa oxy, cho tam giac ABC co A(1;2); B(-1;1); C(5;-1). Tinh Cos AA. \(\dfrac{-1}{\sqrt{5}}\) B.\(\dfrac{1}{\sqrt{5}}\) C. \(\dfrac{-2}{\sqrt{5}}\) ...
Đọc tiếp
1) Trong mat phang toa oxy, cho tam giac ABC co A(1;2); B(-1;1); C(5;-1). Tinh Cos A
A. \(\dfrac{-1}{\sqrt{5}}\) B.\(\dfrac{1}{\sqrt{5}}\) C. \(\dfrac{-2}{\sqrt{5}}\) D. \(\dfrac{2}{\sqrt{5}}\)
