Find the value of λ for which vector (a and b) are perpendicular, where
(i) vector a = 2i + λj + k and vector b = (i - 2j + 3k)
(ii) vector a = 3i - j + 4k and b = -λi + 3j + 3k
(iii) vector a = 2i + 4j - k and vector b = 3i - 2j + λk
(iv) vector a = 3i + 2j - 5k and b = -5j + λk
