The correct option is Option D: f(x)=(5)ˣ.
The function is increasing where its derivative is greater than 0.
for example, f(x) is increasing then f'(x) is greater than 0.
Here f(x) = aˣ
so the dervative of the function
d(f(x))/dx=d(aˣ)/dx
⇒f'(x)= ㏑(a)aˣ
f'(x)>0
⇒㏑(a)aˣ >0
as aˣ is always greater than 0,
⇒㏑(a)>0
⇒a>1
as ㏑(a) is greater than 0 when a >1 and is lesser than when 0<a<1.
checking all the options
Option A. f(x)=(1/5)ˣ here a =1/5<1 so, f(x) is not increasing. Option A is incorrect.
Option B: f(x)=(0.5)ˣ here a =0.5<1 so, f(x) is not increasing. Option B is incorrect.
Option C: f(x)=(1/15)ˣ here a =1/15<1 so, f(x) is not increasing. Option C is incorrect.
Option D: f(x)=(5)ˣ here a =5>1 so, f(x) is increasing. Option A is correct.
Therefore the correct option is Option D: f(x)=(5)ˣ.
Learn more about increasing function
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