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Problem
## EXERCISE 2.2 Prove the following: 2.
3
cos
−
1
x
=
cos
−
1
(
4
x
3
−
3
x
)
,
x
∈
[
1
2
,
1
]
3 \cos ^{-1} x=\cos ^{-1}\left(4 x^{3}-3 x\right), x \in\left[\frac{1}{2}, 1\right]
3
cos
−
1
x
=
cos
−
1
(
4
x
3
−
3
x
)
,
x
∈
[
2
1
,
1
]
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