Lets call the above DETERMINANT D.

D =0

one of the roots of D is x= -9.

find the other roots.

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Guys,

after solving the determinant I get,

x³ - 67x -126 = 0

After this I dont know how to proceed..!! PLZ help

Factorize it. It is easy since you are given one of the roots: 

x³ - 67x -126 = 0

I think that should be x³ - 67x +126 = 0 as x=-9 doesnot satisfy the equation you got. Kindly check it.

So now the equation x³ - 67x +126 = 0

(x+9)(x²-9x+14)=0

(x+9)(x-7)(x-2)=0

So the other roots are 7 and 2

It is also  possible that x=-9 can be a typo. In that case the above answer is correct.