A) 0
B) 1
C) 3
D) -3
Correct Answer: C
Solution :
Given \[{{\cos }^{-1}}x+{{\cos }^{-1}}y+{{\cos }^{-1}}z=3\pi \] \[\because 0\le {{\cos }^{-1}}x\le \pi \] \[\therefore 0\le {{\cos }^{-1}}y\le \pi \]and \[0\le {{\cos }^{-1}}z\le \pi \] Here \[{{\cos }^{-1}}x={{\cos }^{-1}}y={{\cos }^{-1}}z=\pi \] \[\Rightarrow x=y=z=\cos \pi =-1\] \ \[xy+yz+zx\]\[=(-1)(-1)+(-1)(-1)+(-1)(-1)\] \[=1+1+1=3\].You need to login to perform this action.
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