What is the value of det[1, 2, 3; 4, 5, 6; 7, 8, 9]?

Determinants, Adjoint & Inverse · Question 19 of 87

Question 19

MediumOriginal question

What is the value of $\begin{vmatrix}1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9\end{vmatrix}$ ?

-3

Correct answerYour answer

0

Correct answerYour answer

3

Correct answerYour answer

6

Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

Apply $R_3 \to R_3 - R_2$ and $R_2 \to R_2 - R_1$ : both rows become $(3, 3, 3)$ .
Two equal rows make the determinant 0.

Worth noting

Expanding with every sign $+$ gives a non-zero value; the signs must alternate.

Ten questions from Determinants, Adjoint & Inverse, at your own pace.

Ten questions from Determinants, Adjoint & Inverse, at your own pace.