# Logarithms problem

Gold Member
Hey!
I have a question regarding a statement in my physics book. I dont see how
$$|H(f)|_{dB} = - 10log (1+( \frac{f}{f_B})^2)$$

approaches this equation below for big values on f.

$$|H(f)|_{dB} = - 20log ( \frac{f}{f_B})$$

EDIT: I am sorry if this is posted to a wrong sub-forum.

Last edited:

ShayanJ
Gold Member
When f is large, you can ignore 1 and so there only remains $-10 \log{(\frac{f}{f_B})^2}$. Now you can use the property $\log a^n=n\log a$ to get what you want.

Rectifier
Gold Member
When f is large, you can ignore 1 and so there only remains $-10 \log{(\frac{f}{f_B})^2}$. Now you can use the property $\log a^n=n\log a$ to get what you want.
Oh gosh. Thank you for your help :)