Question

   
28/(x+3)+28/(x-3)=7 

Answer 1

ОДЗ
x≠3
x≠-3


$dfrac{28}{x+3} + dfrac{28}{x-3}=7$

общий знаменатель $(x+3)(x-3)$

$28(x-3)+28(x+3)=7(x+3)(x-3)\56x=7(x^2-9)\x^2-8x-9=0\D=100\\x_1=dfrac{8+10}{2}=9;quad x_2=-1$

Answer 2

28/(x+3)+28/(x-3)=7
4(1/(х+3)+1/(х-3))=1
4(х-3+х+3)=(х+3)(х-3)
8х=х²-9
х²-8х-9=0
D=64+36=100=10²
х1=(8+10)/2=9
х2=(8-10)/2=-1