∣x+
1−x
2

​
∣=
2
​
(2x
2
−1)∣cosα+sinα∣=
2
​
(2cos
2
α−1)
∣
N
2
c
o
s
(
α
−
π
4
)
∣
=
N
2
c
o
s
(
2
α
)

α
∈
[
0
;
π
4
]
∪
[
3
π
4
;
π
]
∣N
2
​
cos(α−
4
π
​
)∣=N
2
​
cos(2α) α∈[0;
4
π
​
]∪[
4
3π
​
;π]
1)
α
∈
[
0
;
π
4
]
α∈[0;
4
π
​
]
c
o
s
(
α
−
π
4
)
=
c
o
s
(
2
α
)
…
cos(α−
4
π
​
)=cos(2α)…
2.
α
∈
[
3
π
4
;
π
]
α∈[
4
3π
​
;π]
−
c
o
s
(
α
−
π
4
)
=
c
o
s
(
2
α
)
…
−cos(α−
4
π
​
)=cos(2α)