(Q9)Show that tan
2
θ + tan
4
θ = sec
4
θ - sec
2
θ
L.H.S. = tan
2
θ + tan
4
θ
= tan
2
θ (
+
2
θ)
= tan
2
θ .
2
θ
= (
2
θ - 1) sec
2
θ
=
4
θ –
2
θ = R.H.S
Clear