1.

Prove that vectors (a + b).(a - b) = |a|2 + |b|2 ⇔ a⊥b, where vectors a ≠ 0 and  vectors b ≠ 0.

Answer»

\((\vec{a}+\vec{b}).(\vec{a}-\vec{b})\) = \(|\vec{a}|^2+|\vec{b}|^2\) 

⇒  \(|\vec{a}|^2-|\vec{b}|^2\) =   \(|\vec{a}|^2+|\vec{b}|^2\)

⇒    \(|\vec{b}|\) = 0

Which is not possible hence

\((\vec{a})⊥(\vec{b})\)



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