Show the matrix ⎡⎢⎣l1m1n1l2m2n2l3m3n3⎤⎥⎦ is orthogonal if l21+m21+n21=∑l21=1=∑l22=∑l23 and l1l2+m1m2+n1n2=∑l1l2=0=∑l2l3=∑l3l1
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Solution
Let A=⎡⎢⎣l1m1n1l2m2n2l3m3n3⎤⎥⎦ ∴A′=⎡⎢⎣l1l2l3m1m2m3n1n2n3⎤⎥⎦ Now A.A′=⎡⎢⎣l1m1n1l2m2n2l3m3n3⎤⎥⎦×⎡⎢⎣l1l2l3m1m2m3n1n2n3⎤⎥⎦ =⎡⎢
⎢⎣∑l21∑l1l2∑l3l1∑l1l2∑l22∑l2l3∑l3l1∑l2l3∑l23⎤⎥
⎥⎦=⎡⎢⎣100010001⎤⎥⎦=I