Answer:
Explanation:
Factor the left hand side as a difference of squares:
(
cos
2
θ
+
sin
2
θ
)
(
cos
2
θ
−
sin
2
θ
)
=
cos
2
θ
−
sin
2
θ
Apply the pythagorean identity
cos
2
θ
+
sin
2
θ
=
1
:
1
(
cos
2
θ
−
sin
2
θ
)
=
cos
2
θ
−
sin
2
θ
cos
2
θ
−
sin
2
θ
=
cos
2
θ
−
sin
2
θ
L
H
S
=
R
H
S
Hopefully this helps!