Question Number 102796 by saorey0202 last updated on 11/Jul/20
$$\mathrm{The}\:\mathrm{angle}\:\mathrm{between}\:\mathrm{the}\:\mathrm{vectors} \\ $$$$\mathrm{2}\boldsymbol{\mathrm{i}}+\mathrm{3}\boldsymbol{\mathrm{j}}+\boldsymbol{\mathrm{k}}\:\:\mathrm{and}\:\:\mathrm{2}\boldsymbol{\mathrm{i}}−\boldsymbol{\mathrm{j}}−\boldsymbol{\mathrm{k}}\:\:\mathrm{is} \\ $$
Answered by bramlex last updated on 11/Jul/20
$$\mathrm{cos}\:\beta\:=\:\frac{\overset{\rightarrow} {{a}}.\overset{\rightarrow} {{b}}}{\mid\overset{\rightarrow} {{a}}\mid\:\mid\overset{\rightarrow} {{b}}\mid}\:=\:\frac{\mathrm{4}−\mathrm{3}−\mathrm{1}}{\mid\overset{\rightarrow} {{a}}\mid\:\mid\overset{\rightarrow} {{b}}\mid} \\ $$$$\beta\:=\:\mathrm{90}^{\mathrm{o}} \: \\ $$