By the theory of logs 7^[2x72x can be written as e^[2xln7]e2xln7 ,i.e,
7^[2x]=e^[2xln7]72x=e2xln7.....[1][1]
Therefore, d/dx7^[2x=ddx72x= d/[dx]ddx[e^[2xln7]][e2xln7]
d/dx[e^[2xln7]]ddx[e2xln7]=[e^[2xln7]d/dx[2xln7]][e2xln7ddx[2xln7]] and since ln7ln7 is a constant,
d/dx[2xln7]ddx[2xln7] = 2ln72ln7..... So, d/dx7^[2xddx72x=2ln7[e^[2xln7]]2ln7[e2xln7].......[2][2]
From .....[1][1], e^[2xln7e2xln7= 7^[2x72x so substituting in 2,
d/dx 7^[2xddx72x=2ln7[7^[2x]]2ln7[72x]=ln49[7^[2x]]ln49[72x]. Hope this was helpful.