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JEE Main 202331 JanuaryEvening Shift
Exam
JEE Main
Year
2023
Date
31 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Matrices

JEE Main 2023 · 31 January · Evening Shift · Mathematics · Matrices

Let A = ⌊ a _ ^ i ^ j ⌋ · a _ ij ∈ Z [0, 4], 1 ≤ i, j ≤ 2 . The...

Let A = \left⌊{a}_{\overset{^}{i}\overset{^}{j}}\right⌋ \cdot {a}_{ij} \in Z \cap \left[0, 4\right], 1 \le i, j \le 2. The number of matrices AA such that the sum of all entries is aa prime number p∈(2,13)p \in \left(2, 13\right) is _____ .

Correct answer

0

Step-by-step solution

Given,

A = \left[\begin{cases}{a}_{11} & {a}_{12} \\ {a}_{21} & {a}_{22}\end{cases}\right] \text{ and } {a}_{11}, {a}_{12}, {a}_{21}, {a}_{22} \in \left\{0, 1, 2, 3, 4\right\}

Now given a11+a12+a23+a22={a}_{11} + {a}_{12} + {a}_{23} + {a}_{22} = prime number,

So sum can be, p=3,5,7,11p = 3, 5, 7, 11

Now using multinomial theorem we get,

Sum will be sum of coefficient of x3,x5,x7 and x11{x}^{3}, {x}^{5}, {x}^{7} \text{ and } {x}^{11}in expansion of (x0+x1+x2+x3+x4)4{\left({x}^{0} + {x}^{1} + {x}^{2} + {x}^{3} + {x}^{4}\right)}^{4}

⇒(1−x51−x)4=(1−x5)4(1−x)−4⇒ {\left(\dfrac{1 - {x}^{5}}{1 - x}\right)}^{4} = {\left(1 - {x}^{5}\right)}^{4}{\left(1 - x\right)}^{- 4}

=(Cr14(−x5)r1)(Cr24+r2−1xr2)= \left(C{r}_{1} 4 {\left(- {x}^{5}\right)}^{{r}_{1}}\right)\left(C{r}_{2} 4 + {r}_{2} - 1 {x}^{{r}^{2}}\right)

=Cr13+r24Cr2(−1)r1(x)5r1+r2= Cr13 + {r}_{2} 4 {C}_{r2}{\left(- 1\right)}^{{r}_{1}}{\left(x\right)}^{{}^{5{r}_{1} + {r}_{2}}}

Now taking, 5r1+r2=3,5,7,115{r}_{1} + {r}_{2} = 3, 5, 7, 11

when 5r1+r2=3⇒r1=0,r2=35{r}_{1} + {r}_{2} = 3 ⇒ {r}_{1} = 0, {r}_{2} = 3

when 5r1+r2=5⇒r1=0,r2=55{r}_{1} + {r}_{2} = 5 ⇒ {r}_{1} = 0, {r}_{2} = 5 or r1=1,r2=0{r}_{1} = 1, {r}_{2} = 0

when 5r1+r2=7⇒r1=1,r2=25{r}_{1} + {r}_{2} = 7 ⇒ {r}_{1} = 1, {r}_{2} = 2 or r1=0,r2=7{r}_{1} = 0, {r}_{2} = 7

when 5r1+r2=11⇒r1=0,r2=115{r}_{1} + {r}_{2} = 11 ⇒ {r}_{1} = 0, {r}_{2} = 11 or r1=1,r2=6{r}_{1} = 1, {r}_{2} = 6 or r1=2,r2=1{r}_{1} = 2, {r}_{2} = 1

So, sum of all coefficient =C04×C36+C04C58−C14C03+C04C710−C14C25+C04C1114−C14C69+C24C14= C0 4 \times C3 6 + C0 4 C5 8 - C1 4 C0 3 + C0 4 C7 10 - C1 4 C2 5 + C0 4 C11 14 - C1 4 C6 9 + C2 4 C1 4

=20+56−4+120−40+364−336+24= 20 + 56 - 4 + 120 - 40 + 364 - 336 + 24

=204= 204

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