
Victoria V. answered 05/20/20
15+ Years Experience Teaching / Tutoring Trigonometry
This is very unclear the way it is typed, but the only way it makes sense (and is true) is if I rewrite it as:
logx(xy) - 2 logx(y) = 1 - logx(y)
Properties of logs say we can expand:
logx(x) + logx(y) - 2 logx(y)
By definition, logx(x) = 1
So this becomes 1 + logx(y) - 2 logx(y) and this becomes 1 - logx(y)