Question

памогите мне пожалуйста

Answer 1

$tt1) 7-bsqrt{7} =(sqrt{7})^2-bsqrt{7}=sqrt{7}(sqrt{7}-b)\\ 2) sqrt{12}+sqrt{15}=sqrt{3}cdotsqrt{4}+sqrt{3}cdotsqrt{5} =sqrt{3}(sqrt{4}+sqrt{5})=sqrt{3}(2+sqrt{5})$