1.

If `cos^(-1)x+cos^(-1)y+cos^(-1)z+cos^(-1)t=4pi`, then `x^(2)+y^(2)+z^(2)+t^(2)=`A. `6`B. `4`C. `xy+yz+zt`D. `1-2xyzt`

Answer» Correct Answer - B


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