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Problem
Problem
If
cos
−
1
x
+
cos
−
1
y
+
cos
−
1
z
=
π
\cos^{-1} x + \cos^{-1} y + \cos^{-1} z = \pi
cos
−
1
x
+
cos
−
1
y
+
cos
−
1
z
=
π
, prove that
x
2
+
y
2
+
z
2
+
2
x
y
z
=
1
x^2 + y^2 + z^2 + 2xyz = 1
x
2
+
y
2
+
z
2
+
2
x
y
z
=
1
.
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