The value of
tan 48∘.tan 23∘.tan 42∘.tan 67∘ =
tan48∘.tan23∘.tan42∘.tan67∘
We know that cot(90∘−θ)=tanθ
∴tan48∘.tan23∘.tan42∘.tan67∘
= tan48∘.tan23∘.tan(90∘−48∘).tan(90∘−23∘)
= tan48∘.tan23∘.cot48∘.cot23∘
We also know that tanθ×cotθ=1
∴tan48∘.tan23∘.cot48∘.cot23∘
=tan48∘.cot48∘.tan23∘.cot23∘
=1×1
=1