understand wemen is like:
\displaystyle Substitute\; x=cos\alp, \alp\in[0: ;\: \pi ]Substitutex=cos\alp,\alp∈[0:;π]
\displaystyle Then\; |x+\sqrt{1-x^2}|=\sqrt{2}(2x^2-1)\Leftright |cos\alp +sin\alp |=\sqrt{2}(2cos^2\alp -1)Then∣x+
1−x 2∣= 2(2x 2 −1)\Leftright∣cos\alp+sin\alp∣=
2(2cos
2\alp−1)
\displaystyle |\N {\sqrt{2}}cos(\alp-\frac{\pi}{4})|=\N {\sqrt{2}}cos(2\alp )\Right \alp\in[0\: ;\: \frac{\pi}{4}]\cup [\frac{3\pi}{4}\: ;\: \pi]∣N
2cos(\alp−
4π )∣=N 2cos(2\alp)\Right\alp∈[0;
4π]∪[ 43π;π]1) \displaystyle \alp \in [0\: ;\: \frac{\pi}{4}]\alp∈[0;
4π]\displaystyle cos(\alp -\frac{\pi}{4})=cos(2\alp )\dotscos(\alp−
4π )=cos(2\alp)…
2. \displaystyle \alp\in [\frac{3\pi}{4}\: ;\: \pi]\alp∈[
43π ;π]\displaystyle -cos(\alp -\frac{\pi}{4})=cos(2\alp )\dots−cos(\alp−
4π
)=cos(2\alp)…
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