Question

Помогите пожалуйста с A5 B1 B2

Answer 1

$A5)frac{b}{sqrt{7}} = frac{b*sqrt{7}} {sqrt{7}*sqrt{7}}= frac{bsqrt{7}} {7}\\frac{5}{sqrt{13}+sqrt{3}}= frac{5*(sqrt{13}-sqrt{3})} {(sqrt{13}+sqrt{3})(sqrt{13}-sqrt{3})}= frac{5(sqrt{13}-sqrt{3})}{13-3}= frac{5(sqrt{13}-sqrt{3})} {10}= frac{sqrt{13}-sqrt{3}} {2}$

$B1)sqrt{(2-sqrt{7})^{2}} }+ sqrt{(3-sqrt{7})^{2}}=|2- sqrt{7}|+|3- sqrt{7}|= sqrt{7}-2+3- sqrt{7}=1\\B2)frac{sqrt{5}-sqrt{3}} {sqrt{5}+sqrt{3}}- frac{sqrt{5}+sqrt{3}} {sqrt{5}-sqrt{3}}= frac{(sqrt{5}-sqrt{3})^{2}-(sqrt{5}+sqrt{3})^{2}} {(sqrt{5}+sqrt{3})(sqrt{5}-sqrt{3})}=frac{5-2sqrt{15}+3-5-2sqrt{15}-3}{5-3}=- frac{4sqrt{15}} {2} =-2 sqrt{15}$