Help Potrzebuje pomocy w zad 12 podpunkt D daje naj !!!!

[latex]sqrt{21+4sqrt{5}}=sqrt{21+2*2sqrt{5}}=sqrt{1+20+2*2sqrt{5}}=\ \ =sqrt{1+2*2sqrt{5}+20}=sqrt{1^{2}+2*2sqrt{5}+(2*sqrt{5})^{2}}=\ \ =sqrt{(1+2sqrt{5})^{2}}=|1+2sqrt{5}|=1+2sqsrt{5}[/latex]