Using properties of determinants, prove that |[x+y,x,x],[5x+4y,4x,2x],[10x+8y,8x,3x]|=x^3 - Mathematics

Using properties of determinants, prove that

|[x+y,x,x],[5x+4y,4x,2x],[10x+8y,8x,3x]|=x^3

Solution

To prove:

|[x+y,x,x],[5x+4y,4x,2x],[10x+8y,8x,3x]|=x^3

Taking LHS, we get:

|[x+y,x,x],[5x+4y,4x,2x],[10x+8y,8x,3x]|=|[x,x,x],[5x,4x,2x],[10x,8x,3x]|+|[y,x,x],[4y,4x,2x],[8y,8x,3x]|

=x^3|[1,1,1],[5,4,2],[10,8,3]|+x^2y|[1,1,1],[4,4,2],[8,8,3]|

=x^2|[0,0,1],[3,2,2],[7,5,3]|+0  (Using R1 R1 - R3 and R2 R2 - R3, in the first determinant)

=x^3(15-14)=x^3 (2nd determinant is equal to zero as C1 and C2 are equal)

=RHS

Henced proved

Concept: Properties of Determinants
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