Prove that 

(i) vector |a + b|2 + vector |a + b|2 = 2 vector { |a |2 + |b |2}

 (ii) vector |a + b|2 - vector |a + b|2 = 4 vector (a • b)

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1 Answers

consider, 

vector |a + b|2+ vector |a + b|2 = vector {|a|2 + 2 a • b + | b |2} + vector {| a |2 - 2 a • b + |b|2}

= 2 vector { | a |2 + | b |2

Next consider, 

vector | a + b |2- vector | a + b |2= vector { | a |2 + 2 a • b + | b |2 } - vector { | a |2 - 2 a • b + | b |2

= 4 vector (a • b) 

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