The direction ratios of two straight lines are $\mathbf{l}, \mathbf{m}, \mathbf{n}$ and $l_{1}, m_{1}, n_{1}$. The lines will be perpendicular to each other if. (A) $\frac{l}{l_{1}}=\frac{m}{m_{1}}=\frac{n}{n_{1}}$ (B) $\frac{l}{l_{1}}+\frac{m}{m_{1}}+\frac{n}{n_{1}}=0$ (C) $l l_{1}+m m_{1}+n n_{1}=0$ (D) $l l_{1}+m m_{1}+n n_{1}=1$

Home » The direction ratios of two straight lines are and . The lines will be perpendicular to each other if. (A) (B) (C) (D)

The direction ratios of two straight lines are $\mathbf{l}, \mathbf{m}, \mathbf{n}$ and $l_{1}, m_{1}, n_{1}$ . The lines will be perpendicular to each other if. (A) $\frac{l}{l_{1}}=\frac{m}{m_{1}}=\frac{n}{n_{1}}$ (B) $\frac{l}{l_{1}}+\frac{m}{m_{1}}+\frac{n}{n_{1}}=0$ (C) $l l_{1}+m m_{1}+n n_{1}=0$ (D) $l l_{1}+m m_{1}+n n_{1}=1$

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The direction ratios of two straight lines are $\mathbf{l}, \mathbf{m}, \mathbf{n}$ and $l_{1}, m_{1}, n_{1}$ . The lines will be perpendicular to each other if. (A) $\frac{l}{l_{1}}=\frac{m}{m_{1}}=\frac{n}{n_{1}}$ (B) $\frac{l}{l_{1}}+\frac{m}{m_{1}}+\frac{n}{n_{1}}=0$ (C) $l l_{1}+m m_{1}+n n_{1}=0$ (D) $l l_{1}+m m_{1}+n n_{1}=1$

Sol.
Correct option is (C). $l l_{1}+m m_{1}+n n_{1}=0$

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