خطا
اول شیب خط را به دست میآوریم. $2x - y = 4 \Rightarrow - y = - 2x + 4 \to x - 1 \to y = 2x - 4$ و شیب آن 2 است پس تانژانت آن $\tan \alpha = 2$ است. $\tan \alpha = 2 \to \tan \alpha = \frac{2}{1}$$ \Rightarrow \begin{array}{*{20}{c}}{B{C^2} = A{B^2} + A{C^2} \Rightarrow B{C^2} = {2^2} + {1^2}}\\{B{C^2} = 5 \Rightarrow BC = \sqrt 5 \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\end{array}$$\sin \alpha = \frac{2}{{\sqrt 5 }} \times \frac{{\sqrt 5 }}{{\sqrt 5 }} = \frac{{2\sqrt 5 }}{5}$