If the angle between a line with direction cosine \(\left(\dfrac{-2}{\sqrt{21}},\dfrac{a}{\sqrt{21}},\dfrac{b}{\sqrt{21}}\right)\) and another line with direction cosine \(\left(\dfrac{3}{\sqrt{54}},\dfrac{3}{\sqrt{54}},\dfrac{-6}{\sqrt{54}}\right)\) is 90°, then find the pair of possible values of a and b respectively?
1
4, 1
2
4, 2
3
-4, -2
4
-1, 4