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Mathematics
Problem
In Exercises 5-22, prove the identity. 13.
cos
2
(
t
2
)
=
1
+
sec
t
2
sec
t
\cos ^{2}\left(\frac{t}{2}\right)=\frac{1+\sec t}{2 \sec t}
cos
2
(
2
t
)
=
2
s
e
c
t
1
+
s
e
c
t
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