@Kitonum 

Sorry I realised my mistake. I have to minimize a*x + log2(3+4.2^(-x)+2.2^(-2x)). And I need to minimize it in terms of a where x>0, 0<=a <=1. 

Thanks for your help!

@Kitonum Hi, The base of the logarithm is 2. Also, I need the solution in terms of a not for specific value of a. Is their any method for this?

Thanks for your help!!

@acer Ok the actual question is to minimize a*x + log(3+4.2^(-x) +2.2^(-2x)) where 0<=x<=1 and a is constant.