log7{x^2-9} -log7{9-2x}=1
log7{(x^2-9)/(9-2x)}=1
log7{(x^2-9)/(9-2x)}=log7{7}
(x^2-9)/(9-2x)=7
x^2+14x-72=0
D=b^2-4ac=484
x1,2=(-b±√D)/2a
x1=-18
x2=4
