Đáp án:
$a) \widehat{\left ( d_1,d_2 \right )}=45^{\circ}\\
b)
\widehat{\left ( d_1,d_2 \right )}=90^{\circ}\\$
Giải thích các bước giải:
$a)\overrightarrow{n_{d_1}}=(5;-1)\\
\overrightarrow{n_{d_2}}=(3;2)\\
\Rightarrow \cos\widehat{\left ( d_1,d_2 \right )}=\dfrac{|5.3+(-1).2|}{\sqrt{5^2+(-1)^2}\sqrt{3^2+2^2}}=\dfrac{\sqrt{2}}{2}\\
\Rightarrow \widehat{\left ( d_1,d_2 \right )}=45^{\circ}\\
b)
\overrightarrow{n_{d_1}}=(12;-10)\\
\overrightarrow{u_{d_2}}=(-6;5)\Rightarrow \overrightarrow{n_{d_2}}=(5;6)\\
\Rightarrow \cos\widehat{\left ( d_1,d_2 \right )}=\dfrac{|12.5+(-10).6|}{\sqrt{12^2+(-10)^2}\sqrt{5^2+6^2}}=0\\
\Rightarrow \widehat{\left ( d_1,d_2 \right )}=90^{\circ}\\$
