JEE Main 2015 · 11 Apr · Shift 1 · Mathematics Q64

MathematicsSingle correct+4 / -1Question 64 of 90

If A is a 3×3 matrix such that $|5\cdot\text{adj}A|=5$ , then $|A|$ is equal to :

\pm\dfrac15

±5

±1

\pm\dfrac1{25}

Answer and worked solution

Official answer: A

$|5\,\text{adj}A|=5^3|A|^2=5$ , so $|A|^2=\frac1{25}$ and $|A|=\pm\frac15$ .

JEE Main 2015 · 11 Apr · Shift 1, Mathematics question 64