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Mathematics
Mathematics
Problem
90. Use the cofunction identities and odd-even identities to prove that
cos
(
π
−
x
)
=
−
cos
x
\cos (\pi-x)=-\cos x
cos
(
π
−
x
)
=
−
cos
x
. [Hint:
cos
(
π
−
x
)
=
cos
(
π
/
2
−
(
x
−
π
/
2
)
)
\cos (\pi-x)=\cos (\pi / 2-(x-\pi / 2))
cos
(
π
−
x
)
=
cos
(
π
/2
−
(
x
−
π
/2
))
.]
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