Subjects algebra

Perpendicular Line F1E48F

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1. 题目要求求一条直线的方程,该直线垂直于直线 $3x - 4y = 5$ 并且经过点 $(-2, 1)$。 2. 首先,求已知直线的斜率。将方程 $3x - 4y = 5$ 改写为斜截式: $$3x - 4y = 5 \Rightarrow -4y = -3x + 5 \Rightarrow y = \frac{3}{4}x - \frac{5}{4}$$ 所以已知直线的斜率为 $m_1 = \frac{3}{4}$。 3. 垂直直线的斜率满足 $m_1 \times m_2 = -1$,因此垂直直线的斜率为: $$m_2 = -\frac{1}{m_1} = -\frac{1}{\frac{3}{4}} = -\frac{4}{3}$$ 4. 利用点斜式方程,过点 $(-2, 1)$,斜率为 $m_2 = -\frac{4}{3}$ 的直线方程为: $$y - 1 = -\frac{4}{3}(x + 2)$$ 5. 展开并整理: $$y - 1 = -\frac{4}{3}x - \frac{8}{3}$$ $$y = -\frac{4}{3}x - \frac{8}{3} + 1 = -\frac{4}{3}x - \frac{8}{3} + \frac{3}{3} = -\frac{4}{3}x - \frac{5}{3}$$ 6. 将方程化为一般式: $$y = -\frac{4}{3}x - \frac{5}{3} \Rightarrow 3y = -4x - 5 \Rightarrow 4x + 3y = -5$$ 7. 对比选项,正确答案是 C:$4x + 3y = -5$。