If $(2,-3,6)$ are direction ratios of a line, then a set of direction cosines is

Direction cosines are obtained by dividing the direction ratios by their magnitude. For $(2,-3,6)$, the magnitude is $\sqrt{2^2+(-3)^2+6^2}=\sqrt{49}=7$. Hence the direction cosines are $\left(\dfrac{2}{7},-\dfrac{3}{7},\dfrac{6}{7}\right)$. Option A and B are numerically the same, but A is the simplified standard form; since exactly one option must be correct, A is the intended answer.