cos
−1
x+cos
y+cos
z=π
y=π−cos
z
(xy−
1−x
2
1−y
)=π−cos
xy−
=cos(π−cos
z)
=−cos(cos
=−z
xy+z=
(xy+z)
=(1−x
)(1−y
)
x
y
+z
+2xyz=1−x
−y
+x
+y
+2xyz=1
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