^Pls help^ Question= Evaluate sqrt(19 - 4sqrt21) ...,where sqrt is square root.

Answer 1

√(19-4√21)
since 21 = 19+2, I'd check

(2-√21)^2 = 4-4√21+21 nope
(1-2√21)^2 = 1-4√21+42 nope
(2√3-√7)^2 = 12-4√21+7 aha!