Question

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Answer 1

$|a + b| \: = \: |a - b| \\ squarig \: both \: the \: sides \\ a {}^{2} + b {}^{2} + 2a.b \: \cos( theta) \: = a {}^{2} + b {}^{2} - 2ab \: \cos(theta) \\ 4ab \: cos(theta) = 0 \\ ab \cos(theta) = 0 \\ hene \: theta \: = 90$
a and b are perpendicular to each other...