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Most Important Selected Qs for JEE AdvancedMathematicsVector Algebra

Given a regular tetrahdedron OABC with side length 1 unit. Let D & E are mid points of AB & OC respectively. If DE AC = m n (where m & n are coprime), then ( m + n ) is

Correct answer

3

Step-by-step solution

Let O ( O ), A ( a ), B ( b ) and C ( c )D is a + b 2 and E is c 2 DE AC = ( c -( a + b ) 2 ) ( c - a )= | c |^2 2 - c a 2 - a c 2 - b c 2 + | a |^2 2 + a b 2 = 1- ( 1 2 )- ( 1 2 )- ( 1 2 )+1+ ( 1 2 ) 2 = 1 2 angle between adjacent sides is 3

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