mohon ya jawabannya [tex] \sqrt{19 - 4 \sqrt{21 = } } [/tex] plis bantu jawab ya pake jalan

bismillahirrohmanirrohim
=√19-4√21
=12 + 7 - 4√21
=12+7 -4 √3 x 7
=12 + 7 - 4 √3√7
=12 - 4√3√7+7
=√(2√3-√7)^2
=2√3 - √7