Question Number 79054 by gopikrishnan last updated on 22/Jan/20
$${The}\:{angle}\:{between}\:{the}\:{planes}\:\overset{\rightarrow} {{r}}.\left(\mathrm{2}\overset{\rightarrow} {{i}}+\mathrm{2}\overset{\rightarrow} {{j}}+\mathrm{2}\overset{\rightarrow} {{k}}\right)=\mathrm{4}\:{and}\:\mathrm{4}{x}−\mathrm{2}{y}+\mathrm{2}{z}=\mathrm{15}\:{is} \\ $$