Verified Solution • 2025–26 Session moderate

QJEEM24Ma2078: JEE Main 2024 Mathematics - Class 12 JEEM24Ma2078 Solution: Let be a real matrix such that Then, the system has :

Let AA be a 3×33 \times 3 real matrix such that

A(101)=2(101),A(−101)=4(−101),A(010)=2(010). A\left(\begin{array}{l}1 \\0 \\1\end{array}\right)=2\left(\begin{array}{l}1 \\0 \\1\end{array}\right), A\left(\begin{array}{l}-1 \\0 \\1\end{array}\right)=4\left(\begin{array}{l}-1 \\0 \\1\end{array}\right), A\left(\begin{array}{l}0 \\1 \\0\end{array}\right)=2\left(\begin{array}{l}0 \\1 \\0\end{array}\right) \text {. }

Then, the system (A−3I)(xyz)=(123)(A-3 I)\left(\begin{array}{l}x \\ y \\ z\end{array}\right)=\left(\begin{array}{l}1 \\ 2 \\ 3\end{array}\right) has :

Multiple Choice Options

  • A exactly two solutions
  • B infinitely many solutions
  • C unique solution
  • D no solution

Step-by-Step Verified Solution

 Let A=[x1amp;y1amp;z1x2amp;y2amp;z2x3amp;y3amp;z3]\text { Let } A=\left[\begin{array}{lll}x_1 & y_1 & z_1 \\x_2 & y_2 & z_2 \\x_3 & y_3 & z_3\end{array}\right]

 Given A[101]=[202] ..... (1)\text { Given } A\left[\begin{array}{l}1 \\0 \\1\end{array}\right]=\left[\begin{array}{l}2 \\0 \\2\end{array}\right] \quad \text{ ..... (1)}

∴[x1+z1x2+z2x3+z3]=[202]\therefore\left[\begin{array}{l}\mathrm{x}_1+\mathrm{z}_1 \\\mathrm{x}_2+\mathrm{z}_2 \\\mathrm{x}_3+\mathrm{z}_3\end{array}\right]=\left[\begin{array}{l}2 \\0 \\2\end{array}\right]

∴x1+z1amp;=2.... (2)x2+z2amp;=0.... (3)x3+z3amp;=0.... (4)\begin{aligned}\therefore \mathrm{x}_1+\mathrm{z}_1 & =2 \quad \text{.... (2)}\\\mathrm{x}_2+\mathrm{z}_2 & =0 \quad \text{.... (3)}\\\mathrm{x}_3+\mathrm{z}_3 & =0 \quad \text{.... (4)}\end{aligned}

amp; Given A[−101]=[−404]amp;∴[−x1+z1−x2+z2−x3+z3]=[404]\begin{aligned}& \text { Given } A\left[\begin{array}{l}-1 \\0 \\1\end{array}\right]=\left[\begin{array}{l}-4 \\0 \\4\end{array}\right] \\& \therefore\left[\begin{array}{l}-\mathrm{x}_1+\mathrm{z}_1 \\-\mathrm{x}_2+\mathrm{z}_2 \\-\mathrm{x}_3+\mathrm{z}_3\end{array}\right]=\left[\begin{array}{l}4 \\0 \\4\end{array}\right]\end{aligned}

⇒−x1+z1=−4... (5)−x2+x2=0... (6)−x3+z3=4\begin{array}{r}\Rightarrow-\mathrm{x}_1+\mathrm{z}_1=-4 \quad \text{... (5)}\\-\mathrm{x}_2+\mathrm{x}_2=0 \quad \text{... (6)}\\-\mathrm{x}_3+\mathrm{z}_3=4\end{array}

amp; Given A[010]=[020]amp;∴[y1y2y3]=[020]\begin{aligned}& \text { Given } A\left[\begin{array}{l}0 \\1 \\0\end{array}\right]=\left[\begin{array}{l}0 \\2 \\0\end{array}\right] \\& \therefore\left[\begin{array}{l}\mathrm{y}_1 \\\mathrm{y}_2 \\\mathrm{y}_3\end{array}\right]=\left[\begin{array}{l}0 \\2 \\0\end{array}\right]\end{aligned}

amp;∴y1=0,y2=2,y3=0amp;∴ from (2),(3),(4),(5),(6) and (7)amp;x1=3x,x2=0,x3=−1amp;y1=0,y2=2,y3=0amp;z1=−1,z2=0,z3=3\begin{aligned}& \therefore \mathrm{y}_1=0, \mathrm{y}_2=2, \mathrm{y}_3=0 \\& \therefore \text { from }(2),(3),(4),(5),(6) \text { and }(7) \\& \mathrm{x}_1=3 \mathrm{x}, \mathrm{x}_2=0, \mathrm{x}_3=-1 \\& \mathrm{y}_1=0, \mathrm{y}_2=2, \mathrm{y}_3=0 \\& \mathrm{z}_1=-1, \mathrm{z}_2=0, \mathrm{z}_3=3\end{aligned}

∴A=[3amp;0amp;−10amp;2amp;0−1amp;0amp;3]∴ Now (A−31)[xyz]=[−123]∴[0amp;0amp;−10amp;−1amp;0−1amp;0amp;0][xyz]=[−123][−z−y−x]=[123][z=−1],[y=−2],[x=−3]\begin{gathered}\therefore A=\left[\begin{array}{ccc}3 & 0 & -1 \\0 & 2 & 0 \\-1 & 0 & 3\end{array}\right] \\\therefore \text { Now }(A-31)\left[\begin{array}{l}x \\y \\z\end{array}\right]=\left[\begin{array}{l}-1 \\2 \\3\end{array}\right] \\\therefore\left[\begin{array}{ccc}0 & 0 & -1 \\0 & -1 & 0 \\-1 & 0 & 0\end{array}\right]\left[\begin{array}{l}x \\y \\z\end{array}\right]=\left[\begin{array}{r}-1 \\2 \\3\end{array}\right] \\{\left[\begin{array}{c}-z \\-y \\-x\end{array}\right]=\left[\begin{array}{l}1 \\2 \\3\end{array}\right]} \\{[z=-1],[y=-2],[x=-3]}\end{gathered}

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