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JEE Advanced 2018Paper 2
Exam
JEE Advanced
Year
2018
Paper
Paper 2
Subject
Mathematics
Chapter
Determinants

JEE Advanced 2018 · Paper 2 · Mathematics · Determinants

Let P be a matrix of order 3 × 3 such that all the entries in P are...

Let P be a matrix of order 3×33 \times 3 such that all the entries in P are from the set \left\{- 1, 0,1\right\}$ . Then, the maximum possible value of the determinant of P is _______.

Correct answer

0

Step-by-step solution

∆ = \left|{a1a2a3b1b2b3c1c2c3\begin{cases}{a}_{1} & {a}_{2} & {a}_{3} \\ {b}_{1} & {b}_{2} & {b}_{3} \\ {c}_{1} & {c}_{2} & {c}_{3}\end{cases}\right| = (a1b2c3+a2b3c1+a3b1c2)⏟x\begin{array}{ll}\mathop{\left({a}_{1}{b}_{2}{c}_{3} + {a}_{2}{b}_{3}{c}_{1} + {a}_{3}{b}_{1}{c}_{2}\right)}_{⏟} \\ x\end{array} - (a3b2c1+a2b1c3+a1b3c2)⏟y\begin{array}{ll}\mathop{\left({a}_{3}{b}_{2}{c}_{1} + {a}_{2}{b}_{1}{c}_{3} + {a}_{1}{b}_{3}{c}_{2}\right)}_{⏟} \\ y\end{array}<br/>Nowif<br />Now ifx \le 3andandy \ge - 3<br/>The<br />The∆canbemaximum6butitisnotpossible<br/>becausecan be maximum 6 but it is not possible<br />becausex = 3 ⇒eachtermofeach term ofx = 1<br/>And<br />Andy = -3 ⇒eachtermofeach term ofy = - 1<br/><br />⇒ \mathop{∏}_{i = 1}^{3}{a}_{i}{b}_{i}{c}_{i} = 1andand\mathop{∏}_{i = 1}^{3}{a}_{i}{b}_{i}{c}_{i} = - 1,whichisacontradiction.<br/>Nowforvaluetobe, which is a contradiction.<br />Now for value to be5onethetermsmustbezerobutthatwillmaketwotermszerowhichmeansanswercannotbeone the terms must be zero but that will make two terms zero which means answer cannot be5.Nextpossibilityis. Next possibility is4which can be obtained as \left|\begin{cases}1 & 1 & 1 \\ - 1 & 1 & 1 \\ 1 & - 1 & 1\end{cases}\right| = 1\left(1 + 1\right) - 1\left(- 1 - 1\right) + 1\left(1 - 1\right) = 4
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