Question 8.9.3: Without expanding, show that a-b is a factor of |A| if A= [1......

Without expanding, show that a-b is a factor of |A| if

A=\left[\begin{array}{lll}1 & 1 & 1 \\a & b & c \\a^2 & b^2 & c^2\end{array}\right]
Question Data is a breakdown of the data given in the question above.

Matrix A: [1 1 1; a b c; a^2 b^2 c^2]

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Step 1:
We are given a matrix A with three rows and three columns. We need to find the determinant of this matrix.
Step 2:
We can simplify the calculation by using the property of determinants that states if we add a multiple of one column to another column, the determinant remains the same. In this case, we subtract the first column from the second column.
Step 3:
By subtracting the first column from the second column, we get a new matrix with the same determinant as the original matrix.
Step 4:
Next, we notice that the first column of the new matrix has a common factor of (a-b). We can factor out (a-b) from the first column.
Step 5:
By factoring out (a-b) from the first column, we get a new matrix where the first column is (a-b) times another matrix.
Step 6:
Finally, we see that the determinant of the original matrix A is equal to (a-b) times the determinant of the new matrix. Therefore, (a-b) is a factor of the determinant of matrix A.

Final Answer

\left|\begin{array}{ccc}1 & 1 & 1 \\a & b & c \\a^2 & b^2 & c^2\end{array}\right|=\left|\begin{array}{ccc}0 & 1 & 1 \\a-b & b & c \\a^2-b^2 & b^2 & c^2\end{array}\right| \quad-C_2+C_1 \rightarrow C_1

 

=(a-b)\left|\begin{array}{ccc}0 & 1 & 1 \\ 1 & b & c \\ a+b & b^2 & c^2\end{array}\right| \quad \begin{aligned} & a-b \text { is a common factor } \\ & \text { of column 1 }\end{aligned}

Hence, |A| is equal to a-b times the last determinant, and so a-b is a factor of |A|.

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