Skip to main contentSkip to solution

The value of 1bcbc(b+c)1caca(c+a)1abab(a+b)\begin{vmatrix} 1 & bc & bc(b+c) \\ 1 & ca & ca(c+a) \\ 1 & ab & ab(a+b) \end{vmatrix} is

Solution

Correct Option: 2

1bcbc(b+c)1caca(c+a)1abab(a+b)\begin{vmatrix} 1 & bc & bc(b+c) \\ 1 & ca & ca(c+a) \\ 1 & ab & ab(a+b) \end{vmatrix}


Applying R2R2R1R_2 \to R_2 - R_1 and R3R3R1R_3 \to R_3 - R_1:

=1bcbc(b+c)0cabcca(c+a)bc(b+c)0abbcab(a+b)bc(b+c)= \begin{vmatrix} 1 & bc & bc(b+c) \\ 0 & ca - bc & ca(c+a) - bc(b+c) \\ 0 & ab - bc & ab(a+b) - bc(b+c) \end{vmatrix}


For R2R_2:

cabc=c(ab)ca - bc = c(a - b)

ca(c+a)bc(b+c)ca(c+a) - bc(b+c)

=c(a2+acb2bc)= c(a^2 + ac - b^2 - bc)

=c[(a2b2)+c(ab)]= c[(a^2 - b^2) + c(a - b)]

=c(ab)(a+b+c)= c(a-b)(a+b+c)

For R3R_3:

abbc=b(ac)ab - bc = b(a - c)

ab(a+b)bc(b+c)ab(a+b) - bc(b+c)

=b(a2+abc2bc)= b(a^2 + ab - c^2 - bc)

=b[(a2c2)+b(ac)]= b[(a^2 - c^2) + b(a - c)]

=b(ac)(a+b+c)= b(a-c)(a+b+c)


=1bcbc(b+c)0c(ab)c(ab)(a+b+c)0b(ac)b(ac)(a+b+c)= \begin{vmatrix} 1 & bc & bc(b+c) \\ 0 & c(a-b) & c(a-b)(a+b+c) \\ 0 & b(a-c) & b(a-c)(a+b+c) \end{vmatrix}


Expanding along C1C_1:

=1×c(ab)c(ab)(a+b+c)b(ac)b(ac)(a+b+c)= 1 \times \begin{vmatrix} c(a-b) & c(a-b)(a+b+c) \\ b(a-c) & b(a-c)(a+b+c) \end{vmatrix}

In this 2×22 \times 2 matrix, C2=(a+b+c)×C1C_2 = (a+b+c) \times C_1.

Since two columns are proportional, the determinant equals 0\boxed{0}.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question