PP Presentation
let
a
=
2
p
f
m
t
,
b
=
2
p
f
c
t
s
(
t
)
=
cos
2
p
f
c
t
+
n
a
cos
a
cos
b
cos
(
a
+
b
)
=
cos
a
cos
b
-
sin
a
sin
b
cos
(
a
-
b
)
=
cos
a
cos
b
+
sin
a
sin
b
2
cos
a
cos
b
=
cos
(
a
+
b
)
+
cos
(
a
-
b
)
cos
a
cos
b
=
1
2
cos
(
a
+
b
)
+
cos
(
a
-
b
)
(
)
s
(
t
)
=
cos
2
p
f
c
t
+
n
a
2
cos
(
a
+
b
)
+
cos
(
a
-
b
)
(
)
QED