Let A=⎡⎢⎣100210321⎤⎥⎦ and U1,U2,U3 be column matrices satisfying AU1=⎡⎢⎣100⎤⎥⎦,AU2=⎡⎢⎣230⎤⎥⎦,AU3=⎡⎢⎣231⎤⎥⎦. If U is 3×3 matrix whose columns are U1,U2,U3, then |U|=
A
3
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B
−3
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C
32
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D
2
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Solution
The correct option is C3 A=⎡⎢⎣100210321⎤⎥⎦ Let U1=⎡⎢⎣a1b1c1⎤⎥⎦,U2=⎡⎢⎣a2b2c2⎤⎥⎦ and U3=⎡⎢⎣a3b3c3⎤⎥⎦ Given AU1=⎡⎢⎣100⎤⎥⎦ ⇒a1=1;2a1+b1=0;3a1+2b1+c1=0 simplifying gives a1=1;b1=−2;c1=1 AU2=⎡⎢⎣230⎤⎥⎦ ⇒a2=2;2a2+b2=3;3a2+2b2+c2=0 simplifying gives a2=2;b2=−1;c2=−4 AU3=⎡⎢⎣231⎤⎥⎦ ⇒a3=2;2a3+b3=3;3a3+2b3+c3=1 simplifying gives a3=2;b3=−1;c3=−3 ∴U=⎡⎢⎣122−2−1−11−4−3⎤⎥⎦ |U|=∣∣
∣∣122−2−1−11−4−3∣∣
∣∣=3 Hence, option A.