posted by MIke A .
expand ( 5d-1) 4
Do you mean (5d -1)^4 ?
Square 5d -1 twice.
The first squaring will give you
25d^2 -10d +1
Now square that. There will be more terms next time.
This is not trigonometry
Some people call the nth harmonic the nth ABOVE the fundamental and do not call the fundamental a harmonic. In that case, your answer would be 104/8 = 13 cm
Whoops. Ignore last answer. I posted it in the wrong place