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# The angle between the lines whose direction cosines satisfy the equations $1+m+n=0$ and $1^2=m^2+n^2$ is

$\begin{array}{1 1}(A)\;\large\frac{\pi}{3}\\ (B)\;\large\frac{\pi}{4} \\(C)\;\large\frac{\pi}{6}\\(D)\;\large\frac{\pi}{2} \end{array}$

The angle between the lines whose direction cosines satisfy the equations $1+m+n=0$ and $1^2=m^2+n^2$ is $\large\frac{\pi}{3}$
Hence A is the correct answer.