AA x,y,z in RR f(x+y+z) = f(x)f(y)f(z)!=0 & f(2)=5 , f'(0)=2 then find the value of f'(2) ?

1 Answer
Oct 13, 2016

f'(2)=pm10

Explanation:

f(x+0+0)=f(x)f(0)^2=f(x)->f(0)^2= 1
f(x+delta+0)=f(x)f(delta)f(0)

lim_(delta->0)(f(x+delta)-f(x-delta))/(2delta) = lim_(delta->0)(f(x)f(delta)f(0)-f(x)f(-delta)f(0))/(2delta) =
= f(x)f(0)lim_(delta->0)(f(delta)-f(-delta))/(2delta) = f(x)f(0)f'(0)

but f(0)=pm1 and f'(0) =2 so

f'(x) = f(0)f'(0)f(x) = pm2f(x) and finally

f'(2)=pm10

Note:

(f'(x))/f(x)=pm1/2 then f(x)=C_0e^(pm x/2)