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3 and 4 .Determinants and Matrices
hard
उन पूर्णाकों $x$ की संख्या क्या होगी जो $-3 x^4+\operatorname{det}\left[\begin{array}{ccc}1 & x & x^2 \\ 1 & x^2 & x^4 \\ 1 & x^3 & x^6\end{array}\right]=0$ को संतुष्ट करते हैं
A
$1$
B
$2$
C
$5$
D
$8$
(KVPY-2019)
Solution
(b)
Given, $-3 x^4+\operatorname{det}\left[\begin{array}{ccc}1 & x & x^2 \\ 1 & x^2 & x^4 \\ 1 & x^3 & x^6\end{array}\right]=0$
$x^8+x^5+x^5-x^4-x^7-x^7=3 x^4$
$x^8-2 x^7+2 x^5-4 x^4 =0$
$x^4\left[x^4-2 x^3+2 x-4\right] =0$
$x^4\left[x^3(x-2)+2(x-2)\right]=0$
$x^4\left(x^3+2\right)(x-2)=0$
$\because x$ is an integer, so $x=0,2$.
Standard 12
Mathematics