log (3-x) по основанию1/2 = -2
log1/2;(3-x)=-2
log1/2;(3-x)=-2*log1/2;1/2
log1/2;(3-x)=log1/2;(1/2)^(-2)
log1/2;(3-x)=log1/2;2^2
log1/2;(3-x)=log1/2;4
3-x=4
x=-1