Correct Answer - D
`A A^(T)=9I`
`implies [(1,2,2),(2,1,-2),(a,2,b)][(1,2,a),(2,1,2),(2,-2,b)]=9[(1,0,0),(0,1,0),(0,0,1)]`
`implies [(9,0,a+4+2b),(0,9,2a+2-2b),(a+4+2b,2a+2-2b,a^(2)+4+b^(2))]=[(9,0,0),(0,9,0),(0,0,9)]`
`implies a+4+2b=0, 2a+2-2b=0, a^(2)+4+b^(2)=9`
`implies a=-2, b=-1`