Toán Lớp 10: tính góc giữa 2 vectơ a và b
a) vectơ a(1;-2) ;vectơ b(-1;3)
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Toán Lớp 10: tính góc giữa 2 vectơ a và b
a) vectơ a(1;-2) ;vectơ b(-1;3)
Comments ( 1 )
\quad \cos\left(\overrightarrow{a},\overrightarrow{b}\right) = \dfrac{\overrightarrow{a}.\overrightarrow{b}}{\left|\overrightarrow{a}\right|.\left|\overrightarrow{b}\right|}\\
\Leftrightarrow \cos\left(\overrightarrow{a},\overrightarrow{b}\right) =\dfrac{1.(-1) +(- 2).3}{\sqrt{1^2 + (-2)^2}.\sqrt{(-1)^2 + 3^2}}\\
\Leftrightarrow \cos\left(\overrightarrow{a},\overrightarrow{b}\right) =- \dfrac{7\sqrt2}{10}\\
\Rightarrow \left(\overrightarrow{a},\overrightarrow{b}\right)=171,9^\circ
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