### Question Asked by a Student from EXXAMM.com Team

Q 2178001806.

Assertion : Two spheres of radii r_1 and r_2 cut orthogonally, then radius of the common circle is (r_1r_2)/(sqrt (r_(1)^2 + r-(2)^2) )

Reason : If two spheres x^2 + y^2 + z^2 + 2ux + 2vy + 2wz + d = 0 and x^2 + y^2 + z^2 + 2u' x + 2v' y + 2w' z + d' = 0 cuts orthogonally, then 2u u' + 2v v'+ 2w w' = d + d'

A Both A and R individually true and R is the correct explanation of A
B Both A and R are individually true but R is not the correct explanation of A
C A is true but R is false
D A is false but R is true

#### HINT

(Provided By a Student and Checked/Corrected by EXXAMM.com Team)

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