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Two lines with d.c. (l1, m1, n1) and (l2, m2, n2) are at right angle if(A) l1l2 + m1m2 + n1n2 = 0 (B) l1 = l2, m1 = m2, n1 = n2 (C) l1/l2 = m1/m2 = n1/n2(D) l1l2 = m1m2 = n1n2 |
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Answer» (A) l1l2 + m1m2 + n1n2 = 0 |
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