Solve In(u+5)+In(u-5)=13

Question

I just don't understand 

Answer 1

What we have here is a sum of natural logs.  We can rewrite this as

 

ln((u + 5)(u - 5)) = 13

 

ln(u² - 25) = 13

 

 

The solution to a natural log is the exponent of the base number e as opposed to the base number 10. 

 

e¹³ = u² - 25

 

e¹³ + 25 = u²

 

√(e¹³ + 25) = u