Find λ if

Write the distance of the following plane from the origin :

2x - y + 2z + 1 = 0

Write a vector of magnitude 9 units in the direction of the vector

A family has 2 children. Find the probability that both are boys if it is known that

(i) at least one of the children is a boy

(ii) the elder child is a boy.

Show that the relation S in the set given by S = {(a, b) : a, b ∈ Z, |a - b| is divisible by 4} is an equivalence relation. Find the set of all elements related to 1.