maths log 問題

log(x＋y)=a
log(x-y)=b


log { x^2 -y^2 }^1/2　　　因 log x^y = y log x
=1/2 log { x^2 -y^2 }　　　因 x^2-y^2 = (x＋y)(x-y)
=1/2 log { (x＋y)(x-y) }　　因 log a*b = loga＋logb
=1/2 { log(x＋y) ＋ log(x-y) }
=1/2 ( a＋b )#